Glossary of Unicode Terms

A B C D E F G H I J K L M

This glossary is updated periodically to stay synchronized with changes to various standards maintained by the Unicode Consortium.

See About Unicode Terminology for translations of various terms. There is also an FAQ section on the website.

Abjad. A writing system in which only consonants are indicated. The term “abjad” is derived from the first four letters of the traditional order of the Arabic script: alef, beh, jeem, dal. (See Section 6.1, Writing Systems.)

Abstract Character. A unit of information used for the organization, control, or representation of textual data. (See definition D7 in Section 3.4, Characters and Encoding.)

Abstract Character Sequence. An ordered sequence of one or more abstract characters. (See definition D8 in Section 3.4, Characters and Encoding.)

Abugida. A writing system in which consonants are indicated by the base letters that have an inherent vowel, and in which other vowels are indicated by additional distinguishing marks of some kind modifying the base letter. The term “abugida” is derived from the first four letters of the Ethiopic script in the Semitic order: alf, bet, gaml, dant. (See Section 6.1, Writing Systems.)

Accent Mark. A mark placed above, below, or to the side of a character to alter its phonetic value. (See also diacritic.)

Acrophonic. Denoting letters or numbers by the first letter of their name. For example, the Greek acrophonic numerals are variant forms of such initial letters.

Aksara. (1) In Sanskrit grammar, the term for “letter” in general, as opposed to consonant (vyanjana) or vowel (svara). Derived from the first and last letters of the traditional ordering of Sanskrit letters—“a” and “ksha”. (2) More generally, in Indic writing systems, aksara refers to an orthographic syllable.

Algorithm. A term used in a broad sense in the Unicode Standard, to mean the logical description of a process used to achieve a specified result. This does not require the actual procedure described in the algorithm to be followed; any implementation is conformant as long as the results are the same.

Alphabet. A writing system in which both consonants and vowels are indicated. The term “alphabet” is derived from the first two letters of the Greek script: alpha, beta. (See Section 6.1, Writing Systems.)

Alphabetic Property. Informative property of the primary units of alphabets and/or syllabaries. (See Section 4.10, Letters, Alphabetic, and Ideographic.)

Alphabetic Sorting. (See collation.)

AMTRA. Acronym for Arabic Mark Transient Reordering Algorithm. (See Unicode Standard Annex #53, “Unicode Arabic Mark Rendering.”)

Annotation. The association of secondary textual content with a point or range of the primary text. (The value of a particular annotation is considered to be a part of the “content” of the text. Typical examples include glossing, citations, exemplification, Japanese yomi, and so on.)

ANSI. (1) The American National Standards Institute. (2) The Microsoft collective name for all Windows code pages. Sometimes used specifically for code page 1252, which is a superset of ISO/IEC 8859-1.

Apparatus Criticus. Collection of conventions used by editors to annotate and comment on text.

Arabic Digits. The term "Arabic digits" may mean either the digits in the Arabic script (see Arabic-Indic digits) or the ordinary ASCII digits in contrast to Roman numerals (see European digits). When the term "Arabic digits" is used in Unicode specifications, it means Arabic-Indic digits. See Terminology for Digits for additional information on terminology related to digits.

Arabic-Indic Digits. Forms of decimal digits used in most parts of the Arabic world (for instance, U+0660, U+0661, U+0662, U+0663). Although European digits (1, 2, 3,…) derive historically from these forms, they are visually distinct and are coded separately. (Arabic-Indic digits are sometimes called Indic numerals; however, this nomenclature leads to confusion with the digits currently used with the scripts of India.) Variant forms of Arabic-Indic digits used chiefly in Iran and Pakistan are referred to as Eastern Arabic-Indic digits. (See Section 9.2, Arabic.) See Terminology for Digits for additional information on terminology related to digits.

ASCII. (1) The American Standard Code for Information Interchange, a 7-bit coded character set for information interchange. It is the U.S. national variant of ISO/IEC 646 and is formally the U.S. standard ANSI X3.4. It was proposed by ANSI in 1963 and finalized in 1968. (2) The set of 128 Unicode characters from U+0000 to U+007F, including control codes as well as graphic characters. (3) ASCII has been incorrectly used to refer to various 8-bit character encodings that include ASCII characters in the first 128 code points.

ASCII digits. The digit characters U+0030 to U+0039. Also known as European digits. See Terminology for Digits for additional information on terminology related to digits.

Assigned Character. A code point that is assigned to an abstract character. This refers to graphic, format, control, and private-use characters that have been encoded in the Unicode Standard. (See Section 2.4, Code Points and Characters.)

Assigned Code Point. (See designated code point.)

Atomic Character. A character that is not decomposable. (See decomposable character.)

Base Character. Any graphic character except for those with the General Category of Combining Mark (M). (See definition D51 in Section 3.6, Combination.) In a combining character sequence, the base character is the initial character, which the combining marks are applied to.

Basic Multilingual Plane. Plane 0, abbreviated as BMP.

Bicameral. A script that distinguishes between two cases. (See case.) Most often used in the context of Latin-based alphabets of Europe and elsewhere in the world.

Bidi. Abbreviation of bidirectional, in reference to mixed left-to-right and right-to-left text.

Bidirectional Display. The process or result of mixing left-to-right text and right-to-left text in a single line. (See Unicode Standard Annex #9, “Unicode Bidirectional Algorithm.”)

Big-endian. A computer architecture that stores multiple-byte numerical values with the most significant byte (MSB) values first.

Binary Files. Files containing nontextual information.

Block. A grouping of characters within the Unicode encoding space used for organizing code charts. Each block is a uniquely named, continuous, non-overlapping range of code points, containing a multiple of 16 code points, and starting at a location that is a multiple of 16. A block may contain unassigned code points, which are reserved.

BMP. Acronym for Basic Multilingual Plane.

BMP Character. A Unicode encoded character having a BMP code point. (See supplementary character.)

BMP Code Point. A Unicode code point between U+0000 and U+FFFF. (See supplementary code point.)

BNF. Acronym for Backus-Naur Form, a formal meta-syntax for describing context-free syntaxes. (For details, see Appendix A, Notational Conventions.)

BOCU-1. Acronym for Binary Ordered Compression for Unicode. A Unicode compression scheme that is MIME-compatible (directly usable for e-mail) and preserves binary order, which is useful for databases and sorted lists.

BOM. Acronym for byte order mark.

Bopomofo. An alphabetic script used primarily in the Republic of China (Taiwan) to write the sounds of Mandarin Chinese and some other dialects. Each symbol corresponds to either the syllable-initial or syllable-final sounds; it is therefore a subsyllabic script in its primary usage. The name is derived from the names of its first four elements. More properly known as zhuyin zimu or zhuyin fuhao in Mandarin Chinese.

Boustrophedon. A pattern of writing seen in some ancient manuscripts and inscriptions, where alternate lines of text are laid out in opposite directions, and where right-to-left lines generally use glyphs mirrored from their left-to-right forms. Literally, “as the ox turns,” referring to the plowing of a field.

Braille. A writing system using a series of raised dots to be read with the fingers by people who are blind or whose eyesight is not sufficient for reading printed material. (See Section 21.1, Braille.)

Braille Pattern. One of the 64 (for six-dot Braille) or 256 (for eight-dot Braille) possible tangible dot combinations.

Byte. (1) The minimal unit of addressable storage for a particular computer architecture. (2) An octet. Note that many early computer architectures used bytes larger than 8 bits in size, but the industry has now standardized almost uniformly on 8-bit bytes. The Unicode Standard follows the current industry practice in equating the term byte with octet and using the more familiar term byte in all contexts. (See octet.)

Byte Order Mark. The Unicode character U+FEFF when used to indicate the byte order of a text. (See Section 2.13, Special Characters and Noncharacters, and Section 23.8, Specials.)

Byte Serialization. The order of a series of bytes determined by a computer architecture.

Byte-Swapped. Reversal of the order of a sequence of bytes.

Camelcase. A casing convention for compound terms or identifiers, in which the letters are mostly lowercased, but component words or abbreviations may be capitalized. For example, "ThreeWordTerm" or "threeWordTerm".

Canonical. (1) Conforming to the general rules for encoding—that is, not compressed, compacted, or in any other form specified by a higher protocol. (2) Characteristic of a normative mapping and form of equivalence specified in Chapter 3, Conformance.

Canonical Composition. A step in the algorithm for Unicode Normalization Forms, during which decomposed sequences are replaced by primary composites, where possible. (See definition D115 in Section 3.11, Normalization Forms.)

Canonical Decomposable Character. A character that is not identical to its canonical decomposition. (See definition D69 in Section 3.7, Decomposition.)

Canonical Decomposition. Mapping to an inherently equivalent sequence—for example, mapping ä to a + combining umlaut. (For a full, formal definition, see definition D68 in Section 3.7, Decomposition.)

Canonical Equivalence. The relation between two character sequences whose full canonical decompositions are identical. (See definition D70 in Section 3.7, Decomposition.)

Canonical Equivalent. Two character sequences are said to be canonical equivalents if their full canonical decompositions are identical. (See definition D70 in Section 3.7, Decomposition.)

Canonical Ordering. The order of a combining character sequence that results from the application of the Canonical Ordering Algorithm, a step in the process of normalization of strings. See definition D109 in Section 3.11, Normalization Forms.

Cantillation Mark. A mark that is used to indicate how a text is to be chanted or sung.

Capital Letter. Synonym for uppercase letter. (See case.)

Case. (1) Feature of certain alphabets where the letters have two distinct forms. These variants, which may differ markedly in shape and size, are called the uppercase letter (also known as capital or majuscule) and the lowercase letter (also known as small or minuscule). (2) Normative property of characters, consisting of uppercase, lowercase, and titlecase (Lu, Ll, and Lt). (See Section 4.2, Case.)

Case Folding. The mapping of strings to a particular case form, to facilitate searching and sorting of text. Case foldings may be simple, when the case mappings are required not to change the length of the strings to compare, or full, when the case mappings may change the length of the strings to compare. (See Section 3.13.3, Default Case Folding.)

Case Mapping. The association of the uppercase, lowercase, and titlecase forms of a letter. (See Section 5.18, Case Mappings.)

Case-Ignorable. A character C is defined to be case-ignorable if C has the value MidLetter (ML), MidNumLet (MB), or Single_Quote (SQ) for the Word_Break property or its General_Category is one of Nonspacing_Mark (Mn), Enclosing_Mark (Me), Format (Cf), Modifier_Letter (Lm), or Modifier_Symbol (Sk). (See definition D136 in Section 3.13, Default Case Algorithms.)

Case-Ignorable Sequence. A sequence of zero or more case-ignorable characters. (See definition D137 in Section 3.13, Default Case Algorithms.)

CCC. Short name for the Canonical_Combining_Class property, usually lowercased: ccc.

CCS. (1) Acronym for coded character set. (2) Also used as an acronym for combining character sequence.

Cedilla. A mark originally placed beneath the letter c in French, Portuguese, and Spanish to indicate that the letter is to be pronounced as an s, as in façade. Obsolete Spanish diminutive of ceda, the letter z.

CEF. Acronym for character encoding form.

CES. Acronym for character encoding scheme.

Character. (1) The smallest component of written language that has semantic value; refers to the abstract meaning and/or shape, rather than a specific shape (see also glyph), though in code tables some form of visual representation is essential for the reader’s understanding. (2) Synonym for abstract character. (3) The basic unit of encoding for the Unicode character encoding. (4) The English name for the ideographic written elements of Chinese origin. [See ideograph (2).]

Character Block. (See block.)

Character Class. A set of characters sharing a particular set of properties.

Character Encoding Form. Mapping from a character set definition to the actual code units used to represent the data.

Character Encoding Scheme. A character encoding form plus byte serialization. There are seven character encoding schemes in Unicode: UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32, UTF-32BE, and UTF-32LE.

Character Entity. Expression of the form & for "&" or   for the no-break space. These are found in markup language files like HTML or XML. There are also numerically defined character entities. (See also character escape.)

Character Escape. A numerical expression of the form \uXXXX, \xXXXX or &#xXXXX; where X is a hex digit, or &#dddd; where d is a decimal digit. These are found in programming source code or markup language files (such as HTML or XML).

Character Name. A unique string used to identify each abstract character encoded in the standard. (See definition D4 in Section 3.3, Semantics.)

Character Name Alias. An additional unique string identifier, other than the character name, associated with an encoded character in the standard. (See definition D5 in Section 3.3, Semantics.)

Character Properties. A set of property names and property values associated with individual characters. (See Chapter 4, Character Properties.)

Character Repertoire. The collection of characters included in a character set.

Character Sequence. Synonym for abstract character sequence.

Character Set. A collection of elements used to represent textual information.

Charset. (See coded character set.)

Chillu. Abbreviation for chilaaksharam (singular) (cillakṣaram). Refers to any of a set of sonorant consonants in Malayalam, when appearing in syllable-final position with no inherent vowel.

Choseong. A sequence of one or more leading consonants in Korean.

Chu Hán. The name for Han characters used in Vietnam; derived from hànzì.

Chu Nôm. A demotic script of Vietnam developed from components of Han characters. Its creators used methods similar to those used by the Chinese in creating Han characters.

CJK. Acronym for Chinese, Japanese, and Korean. A variant, CJKV, means Chinese, Japanese, Korean, and Vietnamese.

CJK Unified Ideograph. A Han character that has undergone the process of Han unification (conducted primarily by the Ideographic Research Group) and been encoded as a single ideograph with one or more clearly identified CJK source mappings. CJK unified ideographs have no decomposition mappings, and the set of them in the Unicode Standard is normatively specified by the Unified_Ideograph property.

CLDR. (See Unicode Common Locale Data Repository.)

Coded Character. (See encoded character.)

Coded Character Representation. Synonym for coded character sequence.

Coded Character Sequence. An ordered sequence of one or more code points. Normally, this consists of a sequence of encoded characters, but it may also include noncharacters or reserved code points. (See definition D12 in Section 3.4, Characters and Encoding.)

Coded Character Set. A character set in which each character is assigned a numeric code point. Frequently abbreviated as character set, charset, or code set; the acronym CCS is also used.

Code Page. A coded character set, often referring to a coded character set used by a personal computer—for example, PC code page 437, the default coded character set used by the U.S. English version of the DOS operating system.

Code Point. (1) Any value in the Unicode codespace; that is, the range of integers from 0 to 10FFFF₁₆. (See definition D10 in Section 3.4, Characters and Encoding.) Not all code points are assigned to encoded characters. See code point type. (2) A value, or position, for a character, in any coded character set.

Code Point Type. Any of the seven fundamental classes of code points in the standard: Graphic, Format, Control, Private-Use, Surrogate, Noncharacter, Reserved. (See definition D10a in Section 3.4, Characters and Encoding.)

Code Position. Synonym for code point. Used in ISO character encoding standards.

Code Set. (See coded character set.)

Codespace. (1) A range of numerical values available for encoding characters. (2) For the Unicode Standard, a range of integers from 0 to 10FFFF₁₆. (See definition D9 in Section 3.4, Characters and Encoding.)

Code Unit. The minimal bit combination that can represent a unit of encoded text for processing or interchange. The Unicode Standard uses 8-bit code units in the UTF-8 encoding form, 16-bit code units in the UTF-16 encoding form, and 32-bit code units in the UTF-32 encoding form. (See definition D77 in Section 3.9, Unicode Encoding Forms.)

Code Value. Obsolete synonym for code unit.

Codomain. For a mapping, the codomain is the set of code points or sequences that it maps to, while the domain is the set of values that are mapped. For example, a canonical decomposition is a mapping from a set of code points to a set of sequences; the codomain is the set of canonical equivalent mappings. (See also domain.)

Collation. The process of ordering units of textual information. Collation is usually specific to a particular language. Also known as alphabetizing or alphabetic sorting. Unicode Technical Standard #10, “Unicode Collation Algorithm," defines a complete, unambiguous, specified ordering for all characters in the Unicode Standard.

Combining Character. A character with the General Category of Combining Mark (M). (See definition D52 in Section 3.6, Combination.) (See also nonspacing mark.)

Combining Character Sequence. A maximal character sequence consisting of either a base character followed by a sequence of one or more characters where each is a combining character, zero width joiner, or zero width non-joiner; or a sequence of one or more characters where each is a combining character, zero width joiner, or zero width non-joiner. (See definition D56 in Section 3.6, Combination.)

Combining Class. A numeric value in the range 0..254 given to each Unicode code point, formally defined as the property Canonical_Combining_Class. (See definition D104 in Section 3.11, Normalization Forms.)

Combining Mark. A commonly used synonym for combining character.

Compatibility. (1) Consistency with existing practice or preexisting character encoding standards. (2) Characteristic of a normative mapping and form of equivalence specified in Section 3.7, Decomposition.

Compatibility Character. A character that would not have been encoded except for compatibility and round-trip convertibility with other standards. (See Section 2.3, Compatibility Characters.)

Compatibility Composite Character. Synonym for compatibility decomposable character.

Compatibility Decomposable Character. A character whose compatibility decomposition is not identical to its canonical decomposition. (See definition D66 in Section 3.7, Decomposition.)

Compatibility Decomposition. Mapping to a roughly equivalent sequence that may differ in style. (For a full, formal definition, see definition D65 in Section 3.7, Decomposition.)

Compatibility Equivalence. The relation between two character sequences whose full compatibility decompositions are identical. (See definition D67 in Section 3.7, Decomposition.)

Compatibility Equivalent. Two character sequences are said to be compatibility equivalents if their full compatibility decompositions are identical. (See definition D67 in Section 3.7, Decomposition.)

Compatibility Ideograph. A Han character encoded for compatibility with some East Asian character encoding, but which is not encoded as a CJK unified ideograph. Instead, each compatibility ideograph has a canonical decomposition mapping to a particular CJK unified ideograph.

Compatibility Precomposed Character. Synonym for compatibility decomposable character.

Compatibility Variant. A character that generally can be remapped to another character without loss of information other than formatting.

Composite Character. (See decomposable character.)

Composite Character Sequence. (See combining character sequence.)

Composition Exclusion. A Canonical Decomposable Character which has the property value Composition_Exclusion=True. (Used in the definition of Unicode Normalization Forms.) (See definition D112 in Section 3.11, Normalization Forms.)

Conformance. Adherence to a specified set of criteria for use of a standard. (See Chapter 3, Conformance.)

Confusable. Of similar or identical appearance. When referring to characters in strings, the appearance of confusable characters can make different identifiers hard or impossible to distinguish. (See also Unicode Technical Standard #39, "Unicode Security Mechanisms".)

Conjunct Form. A ligated form representing a consonant conjunct.

Consonant Cluster. A sequence of two or more consonantal sounds. Depending on the writing system, a consonant cluster may be represented by a single character or by a sequence of characters. (Contrast digraph.)

Consonant Conjunct. A sequence of two or more adjacent consonantal letterforms, consisting of a sequence of one or more dead consonants followed by a normal, live consonant letter. A consonant conjunct may be ligated into a single conjunct form, or it may be represented by graphically separable parts, such as subscripted forms of the consonant letters. Consonant conjuncts are associated with the Brahmi family of Indic scripts. (See Section 12.1, Devanagari.)

Contextual Variant. A text element can have a presentation form that depends on the textual context in which it is rendered. This presentation form is known as a contextual variant.

Contributory Property. A simple property defined merely to make the statement of a rule defining a derived property more compact or general. (See definition D35a in Section 3.5, Properties.)

Control Codes. The 65 characters in the ranges U+0000..U+001F and U+007F..U+009F. Also known as control characters.

Core Specification. The central part of the Unicode Standard–the portion which up until Version 5.0 was published as a separate book. Starting with Version 5.2, this part of the standard has been published online only, rather than as a book. The core specification consists of the general introduction and framework for the standard, the formal conformance requirements, many implementation guidelines, and extensive chapters providing information about all the encoded characters, organized by script or by significant classes of characters. Formally, a version of the Unicode Standard is defined by an edition of this core specification, together with the Code Charts, Unicode Standard Annexes, and the Unicode Character Database

Cursive. Writing where the letters of a word are connected.

Dasia. Greek term for rough breathing mark, used in polytonic Greek character names.

DBCS. Acronym for double-byte character set.

Dead Consonant. An Indic consonant character followed by a virama character. This sequence indicates that the consonant has lost its inherent vowel. (See Section 12.1, Devanagari .)

Decimal Digits. Digits that can be used to form decimal-radix numbers.

Decomposable Character. A character that is equivalent to a sequence of one or more other characters, according to the decomposition mappings found in the Unicode Character Database, and those described in Section 3.12, Conjoining Jamo Behavior. It may also be known as a precomposed character or a composite character. (See definition D63 in Section 3.7, Decomposition.)

Decomposition. (1) The process of separating or analyzing a text element into component units. These component units may not have any functional status, but may be simply formal units—that is, abstract shapes. (2) A sequence of one or more characters that is equivalent to a decomposable character. (See definition D64 in Section 3.7, Decomposition.)

Decomposition Mapping. A mapping from a character to a sequence of one or more characters that is a canonical or compatibility equivalent and that is listed in the character names list or described in Section 3.12, Conjoining Jamo Behavior. (See definition D62 in Section 3.7, Decomposition.)

Default Ignorable. Default ignorable code points are those that should be ignored by default in rendering unless explicitly supported. They have no visible glyph or advance width in and of themselves, although they may affect the display, positioning, or adornment of adjacent or surrounding characters. (See Section 5.21, Ignoring Characters in Processing.)

Defective Combining Character Sequence. A combining character sequence that does not start with a base character. (See definition D57 in Section 3.6, Combination.)

Demotic Script. (1) A script or a form of a script used to write the vernacular or common speech of some language community. (2) A simplified form of the ancient Egyptian hieratic writing.

Dependent Vowel. A symbol or sign that represents a vowel and that is attached or combined with another symbol, usually one that represents a consonant. For example, in writing systems based on Arabic, Hebrew, and Indic scripts, vowels are normally represented as dependent vowel signs.

Deprecated. Of a coded character or a character property, strongly discouraged from use. (Not the same as obsolete.)

Deprecated Character. A coded character whose use is strongly discouraged. Such characters are retained in the standard, indefinitely but should not be used. (See definition D13 in Section 3.4, Characters and Encoding.)

Designated Code Point. Any code point that has either been assigned to an abstract character (assigned characters) or that has otherwise been given a normative function by the standard (surrogate code points and noncharacters). This definition excludes reserved code points. Also known as assigned code point. (See Section 2.4 Code Points and Characters.)

Deterministic Comparison. A string comparison in which strings that do not have identical contents will compare as unequal. There are two main varieties, depending on the sense of "identical:" (a) binary equality, or (b) canonical equivalence. This is a property of the comparison mechanism, and not of the sorting algorithm. Also known as stable (or semi-stable) comparison.

Deterministic Sort. A sort algorithm which returns exactly the same output each time it is applied to the same input. This is a property of the sorting algorithm, and not of the comparison mechanism. For example, a randomized Quicksort (which picks a random element as the pivot element, for optimal performance) is not deterministic. Multiprocessor implementations of a sort algorithm may also not be deterministic.

Diacritic. (1) A mark applied or attached to a symbol to create a new symbol that represents a modified or new value. (2) A mark applied to a symbol irrespective of whether it changes the value of that symbol. In the latter case, the diacritic usually represents an independent value (for example, an accent, tone, or some other linguistic information). Also called diacritical mark or diacritical. (See also combining character and nonspacing mark.)

Diaeresis. Two horizontal dots over a letter, as in naïve. The diaeresis is not distinguished from the umlaut in the Unicode character encoding. (See umlaut.)

Dialytika. Greek term for diaeresis or trema, used in Greek character names.

Digits. (See Arabic digits, European digits, and Indic digits.) See Terminology for Digits for additional information on terminology related to digits.

Digraph. A pair of signs or symbols (two graphs), which together represent a single sound or a single linguistic unit. The English writing system employs many digraphs (for example, th, ch, sh, qu, and so on). The same two symbols may not always be interpreted as a digraph (for example, cathode versus cathouse). When three signs are so combined, they are called a trigraph. More than three are usually called an n-graph.

Dingbats. Typographical symbols and ornaments.

Diphthong. A pair of vowels that are considered a single vowel for the purpose of phonemic distinction. One of the two vowels is more prominent than the other. In writing systems, diphthongs are sometimes written with one symbol and sometimes with more than one symbol (for example, with a digraph).

Direction. (See paragraph direction.)

Directionality Property. A property of every graphic character that determines its horizontal ordering as specified in Unicode Standard Annex #9, “Unicode Bidirectional Algorithm.” (See Section 4.4, Directionality.)

Display Cell. A rectangular region on a display device within which one or more glyphs are imaged.

Display Order. The order of glyphs presented in text rendering. (See logical order and Section 2.2, Unicode Design Principles.)

Domain. 1. For a mapping, the domain is the set of code points or sequences that are mapped, while the codomain is the set of values they are mapped to. For example, a canonical decomposition is a mapping from a set of code points to a set of sequences; the domain is the entire Unicode codespace. (See also codomain.) 2. A realm of administrative autonomy, authority or control in the Internet, identified by a domain name.

Domain Name. The part of a network address that identifies it as belonging to a particular domain. (Oxford Languages definition.) A domain name is a string of characters. The rules for how Unicode characters can be used in domain names is the concern of IDNA and of UTS #46, Unicode IDNA Compatibility Processing.

Double-Byte Character Set. One of a number of character sets defined for representing Chinese, Japanese, or Korean text (for example, JIS X 0208-1990). These character sets are often encoded in such a way as to allow double-byte character encodings to be mixed with single-byte character encodings. Abbreviated DBCS. (See also multibyte character set.)

Ductility. The ability of a cursive font to stretch or compress the connective baseline to effect text justification.

Dynamic Composition. Creation of composite forms such as accented letters or Hangul syllables from a sequence of characters.

EBCDIC. Acronym for Extended Binary-Coded Decimal Interchange Code. A group of coded character sets used on mainframes that consist of 8-bit coded characters. EBCDIC coded character sets reserve the first 64 code points (x00 to x3F) for control codes, and reserve the range x41 to xFE for graphic characters. The English alphabetic characters are in discontinuous segments with uppercase at xC1 to xC9, xD1 to xD9, xE2 to xE9, and lowercase at x81 to x89, x91 to x99, xA2 to xA9.

ECCS. Acronym for extended combining character sequence.

EGC. Acronym for extended grapheme cluster.

Embedding. A concept relevant to bidirectional behavior. (See Unicode Standard Annex #9, “Unicode Bidirectional Algorithm,” for detailed terminology and definitions.)

Emoji. (1) The Japanese word for "pictograph." (2) Certain pictographic and other symbols encoded in the Unicode Standard that are commonly given a colorful or playful presentation when displayed on devices. Many of the emoji in Unicode were originally encoded for compatibility with Japanese telephone symbol sets. (3) Colorful or playful symbols which are not encoded as characters but which are widely implemented as graphics. (See pictograph.)

Emoticon. A symbol added to text to express emotional affect or reaction—for example, sadness, happiness, joking intent, sarcasm, and so forth. Emoticons are often expressed by a conventional kind of "ASCII art," using sequences of punctuation and other symbols to portray likenesses of facial expressions. In Western contexts these are often turned sideways, as :-) to express a happy face; in East Asian contexts other conventions often portray a facial expression without turning, as ^-^. Rendering systems often recognize conventional emoticon sequences and display them as colorful or even animated glyphs in text. There is also a set of dedicated pictographic symbols—mostly representing different facial expressions—encoded as characters in the Unicode Standard. (See pictograph.)

Encapsulated Text. (1) Plain text surrounded by formatting information. (2) Text recoded to pass through narrow transmission channels or to match communication protocols.

Enclosing Mark. A nonspacing mark with the General Category of Enclosing Mark (Me). (See definition D54 in Section 3.6, Combination.) Enclosing marks are a subclass of nonspacing marks that surround a base character, rather than merely being placed over, under, or through it.

Encoded Character. An association (or mapping) between an abstract character and a code point. (See definition D11 in Section 3.4, Characters and Encoding.) By itself, an abstract character has no numerical value, but the process of “encoding a character” associates a particular code point with a particular abstract character, thereby resulting in an “encoded character.”

Encoding Form. (See character encoding form.)

Encoding Scheme. (See character encoding scheme.)

Equivalence. In the context of text processing, the process or result of establishing whether two text elements are identical in some respect.

Equivalent Sequence. (See canonical equivalent.)

Escape Sequence. A sequence of bytes that is used for code extension. The first byte in the sequence is escape (hex 1B).

EUDC. Acronym for end-user defined character. A character defined by an end user, using a private-use code point, to represent a character missing in a particular character encoding. These are common in East Asian implementations.

European Digits. Forms of decimal digits first used in Europe and now used worldwide. Historically, these digits were derived from the Arabic digits; they are sometimes called “Arabic numerals,” but this nomenclature leads to confusion with the real Arabic-Indic digits. Also called "Western digits" and "Latin digits." See Terminology for Digits for additional information on terminology related to digits.

Extended Base. Any base character, or any standard Korean syllable block. (See definition D51a in Section 3.6, Combination.)

Extended Combining Character Sequence. A maximal character sequence consisting of either an extended base followed by a sequence of one or more characters where each is a combining character, zero width joiner, or zero width non-joiner; or a sequence of one or more characters where each is a combining character, zero width joiner, or zero width non-joiner. Abbreviated as ECCS. (See definition D56a in Section 3.6, Combination.)

Extended Grapheme Cluster. The text between extended grapheme cluster boundaries as specified by Unicode Standard Annex #29, "Unicode Text Segmentation." Abbreviated as EGC. (See definition D61 in Section 3.6, Combination.)

Fancy Text. (See rich text.)

Fixed Position Class. A subset of the range of numeric values for combining classes—specifically, any value in the range 10..199. (See definition D105 in Section 3.11, Normalization Forms.)

Floating (diacritic, accent, mark). (See nonspacing mark.)

Folding. An operation that maps similar characters to a common target, such as uppercasing or lowercasing a string. Folding operations are most often used to temporarily ignore certain distinctions between characters.

Font. A collection of glyphs used for the visual depiction of character data. A font is often associated with a set of parameters (for example, size, posture, weight, and serifness), which, when set to particular values, generate a collection of imagable glyphs.

Format Character. A character that is inherently invisible but that has an effect on the surrounding characters.

Format Code. Synonym for format character.

Format Control Character. Synonym for format character.

Formatted Text. (See rich text.)

FSS-UTF. Acronym for File System Safe UCS Transformation Format, published by the X/Open Company Ltd., and intended for the UNIX environment. Now known as UTF-8.

Full Composition Exclusion. A Canonical Decomposable Character which has the property value Full_Composition_Exclusion=True. (Used in the definition of Unicode Normalization Forms.) (See definition D113 in Section 3.11, Normalization Forms.)

Fullwidth. Characters of East Asian character sets whose glyph image extends across the entire character display cell. In legacy character sets, fullwidth characters are normally encoded in two or three bytes. The Japanese term for fullwidth characters is zenkaku.

FVS. Acronym for Mongolian Free Variation Selector.

G11n. (See globalization.)

GC. 1. Acronym for grapheme cluster. 2. Short name for the General_Category property, usually lowercased: gc.

GCGID. Acronym for Graphic Character Global Identifier. These are listed in the IBM document Character Data Representation Architecture, Level 1, Registry SC09-1391.

General Category. Partition of the characters into major classes such as letters, punctuation, and symbols, and further subclasses for each of the major classes. (See Section 4.5, General Category.)

Generative. Synonym for productive.

Globalization. (1) The overall process for internationalization and localization of software products. (2) a synonym for internationalization. Also known by the abbreviation "g11n". Note that the meaning of "globalization" which is relevant to software products should be distinguished from the more widespread use of "globalization" in the context of economics. (See internationalization, localization.)

Glyph. (1) An abstract form that represents one or more glyph images. (2) A synonym for glyph image. In displaying Unicode character data, one or more glyphs may be selected to depict a particular character. These glyphs are selected by a rendering engine during composition and layout processing. (See also character.)

Glyph Code. A numeric code that refers to a glyph. Usually, the glyphs contained in a font are referenced by their glyph code. Glyph codes may be local to a particular font; that is, a different font containing the same glyphs may use different codes.

Glyph Identifier. Similar to a glyph code, a glyph identifier is a label used to refer to a glyph within a font. A font may employ both local and global glyph identifiers.

Glyph Image. The actual, concrete image of a glyph representation having been rasterized or otherwise imaged onto some display surface.

Glyph Metrics. A collection of properties that specify the relative size and positioning along with other features of a glyph.

Grapheme. (1) A minimally distinctive unit of writing in the context of a particular writing system. For example, ‹b› and ‹d› are distinct graphemes in English writing systems because there exist distinct words like big and dig. Conversely, a lowercase italiform letter a and a lowercase Roman letter a are not distinct graphemes because no word is distinguished on the basis of these two different forms. (2) What a user thinks of as a character.

Grapheme Base. A character with the property Grapheme_Base, or any standard Korean syllable block. (See definition D58 in Section 3.6, Combination.)

Grapheme Cluster. The text between grapheme cluster boundaries as specified by Unicode Standard Annex #29, "Unicode Text Segmentation." (See definition D60 in Section 3.6, Combination.) A grapheme cluster represents a horizontally segmentable unit of text, consisting of some grapheme base (which may consist of a Korean syllable) together with any number of nonspacing marks applied to it.

Grapheme Extender. A character with the property Grapheme_Extend. (See definition D59 in Section 3.6, Combination.) Grapheme extender characters consist of all nonspacing marks, zero width joiner, zero width non-joiner, and a small number of spacing marks.

Graphic Character. A character with the General Category of Letter (L), Combining Mark (M), Number (N), Punctuation (P), Symbol (S), or Space Separator (Zs). (See definition D50 in Section 3.6. Combination.)

Guillemet. Punctuation marks resembling small less-than and greater-than signs, used as quotation marks in French and other languages. (See “Language-Based Usage of Quotation Marks” in Section 6.2, General Punctuation.)

Halant. A preferred Hindi synonym for a virama. It literally means killer, referring to its function of killing the inherent vowel of a consonant letter. (See virama.)

Half-Consonant Form. In the Devanagari script and certain other scripts of the Brahmi family of Indic scripts, a dead consonant may be depicted in the so-called half-form. This form is composed of the distinctive part of a consonant letter symbol without its vertical stem. It may be used to create conjunct forms that follow a horizontal layout pattern. Also known as half-form.

Halfwidth. Characters of East Asian character sets whose glyph image occupies half of the character display cell. In legacy character sets, halfwidth characters are normally encoded in a single byte. The Japanese term for halfwidth characters is hankaku.

Han Characters. Ideographic characters of Chinese origin. (See Section 18.1, Han.)

Hangul. The name of the script used to write the Korean language.

Hangul Syllable. (1) Any of the 11,172 encoded characters of the Hangul Syllables character block, U+AC00..U+D7A3. Also called a precomposed Hangul syllable to clearly distinguish it from a Korean syllable block. (2) Loosely speaking, a Korean syllable block.

Hanja. The Korean name for Han characters; derived from the Chinese word hànzì.

Hankaku. (See halfwidth.)

Han Unification. The process of identifying Han characters that are in common among the writing systems of Chinese, Japanese, Korean, and Vietnamese.

Hànzì. The Mandarin Chinese name for Han characters.

Harakat. Marks used in the Arabic script to indicate vocalization with short vowels. A subtype of tashkil.

Hasant. The Bangla name for halant. (See virama.)

Higher-Level Protocol. Any agreement on the interpretation of Unicode characters that extends beyond the scope of this standard. Note that such an agreement need not be formally announced in data; it may be implicit in the context. (See definition D16 in Section 3.4, Characters and Encoding.)

High-Surrogate Code Point. A Unicode code point in the range U+D800 to U+DBFF. (See definition D71 in Section 3.8, Surrogates.)

High-Surrogate Code Unit. A 16-bit code unit in the range D800₁₆ to DBFF₁₆, used in UTF-16 as the leading code unit of a surrogate pair. Also known as a leading surrogate. (See definition D72 in Section 3.8, Surrogates.)

Hiragana (ひらがな). One of two standard syllabaries associated with the Japanese writing system. Hiragana syllables are typically used in the representation of native Japanese words and grammatical particles, or are used as a fallback representation of other words when the corresponding kanji is either difficult to remember or obscure. (See also katakana.)

HTML. HyperText Markup Language. A text description language related to SGML; it mixes text format markup with plain text content to describe formatted text. HTML is ubiquitous as the source language for Web pages on the Internet. Starting with HTML 4.0, the Unicode Standard functions as the reference character set for HTML content. (See also SGML.)

I18n. (See internationalization.)

IANA. Acronym for Internet Assigned Numbers Authority.

ICU. Acronym for International Components for Unicode, an Open Source set of C/C++ and Java libraries for Unicode and software internationalization support. For information, see https://icu.unicode.org/

Ideograph (or ideogram). (1) Any symbol that primarily denotes an idea or concept in contrast to a sound or pronunciation—for example, ♻, which denotes the concept of recycling by a series of bent arrows. (2) A generic term for the unit of writing of a logosyllabic writing system. In this sense, ideograph (or ideogram) is not systematically distinguished from logograph (or logogram). (3) A term commonly used to refer specifically to Han characters, equivalent to the Chinese, Japanese, or Korean terms also sometimes used: hànzì, kanji, or hanja. (See logograph, pictograph, sinogram.)

Ideographic Property. Informative property of characters that are ideographs. (See Section 4.10, Letters, Alphabetic, and Ideographic.)

Ideographic Variation Sequence. A variation sequence registered in the Ideographic Variation Database. The registration of ideographic variation sequences is subject to the rules specified in Unicode Technical Standard #37, "Unicode Ideographic Variation Database." The base character for an ideographic variation sequence must be an ideographic character, and it makes use of a variation selector in the range U+E0100..U+E01EF. The term ideographic variation sequence is sometimes abbreviated as "IVS".

IDN. (See Internationalized Domain Name.)

IDNA (1) The IDNA2008 protocol for IDNs defined in RFCs 5891, 5892, 5893 and 5894. The protocol categorizes characters (for example as PVALID or DISALLOWED) based on Unicode properties as described in RFC 5892. (For the range of valid code points for each Unicode version, see the data file for the derived IDNA2008_Category property.) (2) The earlier IDNA2003 protocol. (See IDNA Compatibility Processing for differences between IDNA2003 and IDNA2008.)

IDNA Compatibility Processing. (See Unicode Technical Standard #46, "Unicode IDNA Compatibility Processing".)

IDNA2003. (See IDNA (2).)

IDNA2008. (See IDNA (1).)

IICore. A subset of common-use CJK unified ideographs, defined as the fixed collection 370 IICore in ISO/IEC 10646. This subset contains 9,810 ideographs and is intended for common use in East Asian contexts, particularly for small devices that cannot support the full range of CJK unified ideographs encoded in the Unicode Standard.

Ijam. Diacritical marks applied to basic letter forms to derive new (usually consonant) letters for extended Arabic alphabets. For example, see the three dots below which appear in the letter peh: پ Ijam marks are not separately encoded as combining marks in the Unicode Standard, but instead are integral parts of each atomically encoded Arabic letter. Contrast tashkil. See also Section 9.2, Arabic.

Ill-Formed Code Unit Sequence. A code unit sequence that does not follow the specification of a Unicode encoding form. (See definition D84 in Section 3.9, Unicode Encoding Forms.)

Ill-Formed Code Unit Subsequence. A non-empty subsequence of a Unicode code unit sequence X which does not contain any code units which also belong to any minimal well-formed subsequence of X. (See definition D84a in Section 3.9, Unicode Encoding Forms.)

IME. (See Input Method Editor.)

In-Band. An in-band channel conveys information about text by embedding that information within the text itself, with special syntax to distinguish it. In-band information is encoded in the same character set as the text, and is interspersed with and carried along with the text data. Examples are XML and HTML markup.

Independent Vowel. In Indic scripts, certain vowels are depicted using independent letter symbols that stand on their own. This is often true when a word starts with a vowel or a word consists of only a vowel.

Indic Digits. Forms of decimal digits used in various Indic scripts (for example, Devanagari: U+0966, U+0967, U+0968, U+0969). Arabic digits (and, eventually, European digits) derive historically from these forms. See Terminology for Digits for additional information on terminology related to digits.

Informative. Information in this standard that is not normative but that contributes to the correct use and implementation of the standard.

Inherent Vowel. In writing systems based on a script in the Brahmi family of Indic scripts, a consonant letter symbol normally has an inherent vowel, unless otherwise indicated. The phonetic value of this vowel differs among the various languages written with these writing systems. An inherent vowel is overridden either by indicating another vowel with an explicit vowel sign or by using virama to create a dead consonant.

Inner Caps. Mixed case format where an uppercase letter is in a position other than first in the word—for example, “G” in the Name “McGowan.”

Input Method Editor (IME). A UI-based method of inputting characters with more flexibility and range than possible for a traditional keyboard. An IME may use keystrokes, phonetic spelling or touch screen input to select characters from a candidate list, or to select from partial or complete candidate words.

Intellectual Property. A work or invention that is the result of creativity, such as a manuscript or a design, to which one has rights and for which one may apply for a patent, copyright, trademark, etc. (Oxford Languages definition.) Note that the concept of intellectual property, while relevant to the Unicode Standard and its licensing, is distinct from the usual sense of property in the standard, as for character properties, alphabetic property, ideographic property, script property, etc.

Internationalization. The process of designing and implementing a software product so that it can be easily localized, with few if any structural changes. Ideally, an internationalized software product can be localized simply by translating messages and other text displayed to a user, and by adapting icons and other visual elements. An "internationalized" software product is also known as a "localizable" product. Also known by the abbreviation "i18n" and the term "World-Readiness". (See localization, globalization.)

Internationalized Domain Name (IDN). A domain name using at least one character outside the ASCII range. (See also IDNA.)

IPA. (1) The International Phonetic Alphabet. (2) The International Phonetic Association, which defines and maintains the International Phonetic Alphabet.

IRG. Acronym for Ideographic Research Group, a subgroup of ISO/IEC JTC1/SC2/WG2. (See Appendix E, Han Unification History.)

ISCII. Acronym for Indian Script Code for Information Interchange.

ISO 10646. (See ISO/IEC 10646.)

ISO/IEC 10646. A character encoding standard maintained by ISO in synchronization with the Unicode Standard.

Jamo. The Korean name for a single letter of the Hangul script. Jamos are used to form Hangul syllables.

Joiner. An invisible character that affects the joining behavior of surrounding characters. (See Section 9.2, Arabic, and “Cursive Connection” in Section 23.2, Layout Controls.)

Jongseong. A sequence of one or more trailing consonants in Korean.

JTC1. The Joint Technical Committee 1 of the International Organization for Standardization and the International Electrotechnical Commission responsible for information technology standardization.

Jungseong. A sequence of one or more vowels in Korean.

Kana. A collective term for the two syllabic scripts used (along with kanji and romaji) by the Japanese writing system. The two forms are hiragana and katakana.

Kanji (漢字). The Japanese name for Han characters; derived from the Chinese word hànzì. Also romanized as kanzi.

Katakana (カタカナ). One of two standard syllabaries associated with the Japanese writing system. Katakana syllables are typically used in representation of borrowed vocabulary (other than that of Chinese origin), some plant or animal names, sound-symbolic interjections, emphasis, or for phonetic representation of “difficult” kanji characters in Japanese. (See also hiragana.)

Kerning. (1) Changing the space between certain pairs of letters to improve the appearance of the text. (2) The process of mapping from pairs of glyphs to a positioning offset used to change the space between letters.

Korean Syllable Block. A sequence of Korean jamos, consisting of one or more leading consonants followed by one or more vowels followed by zero or more trailing consonants, or any canonically equivalent sequence including a precomposed Hangul syllable. In regular expression notation: L L* V V* T*. Also called a standard Korean syllable block. (See Section 3.12, Conjoining Jamo Behavior.)

L10n. (See localization.)

Layout Control. Synonym for format character. The term layout control is often used when the format character(s) in question affect the overall layout or rendering of text. See Section 23.2, Layout Controls.

LDML. (See Unicode Locale Data Markup Language.)

Leading Consonant. (1) In Korean, a jamo character with the Hangul_Syllable_Type property value Leading_Jamo (in the range U+1100..U+1159 or U+115F hangul choseong filler). Abbreviated as L. (See definition D122 in Section 3.12, Conjoining Jamo Behavior.) (2) Any initial consonant in a syllable.

Leading Surrogate. Synonym for high-surrogate code unit.

Letter. (1) An element of an alphabet. In a broad sense, it includes elements of syllabaries and ideographs. (2) Informative property of characters that are used to write words.

Ligature. A glyph representing a combination of two or more characters. In the Latin script, there are only a few in modern use, such as the ligatures between “f” and “i” or “f” and “l”. Other scripts make use of many ligatures, depending on the font and style.

Little-endian. A computer architecture that stores multiple-byte numerical values with the least significant byte (LSB) values first.

Localization. (1) The process of adapting a software product to use the languages and conventions suitable for a local market, such as adapting an English US software product to work in Spanish for Argentina. (2) The management of software product translation, which includes extraction of translatable text, management of translations, and generation of language resource modules. Also known by the abbreviation "L10n". Localization produces "localized" software products. (See internationalization, globalization.)

Logical Order. The order in which text is stored in the memory representation. For the most part, logical order corresponds to the typing order and the phonetic order. (See display order and Section 2.2, Unicode Design Principles.)

Logical Store. Memory representation.

Logograph (or logogram). (1) Any symbol that primarily represents a word (or morpheme) in contrast to a sound or pronunciation. (2) A generic term for the unit of writing of a logosyllabic writing system. In this sense, logograph (or logogram) is not systematically distinguished from ideograph (or ideogram). (See ideograph, pictograph.)

Logosyllabary. A writing system in which the units are used primarily to write words and/or morphemes of words, with some subsidiary usage to represent just syllabic sounds. The best example is the Han script.

Lowercase. (See case.)

Low-Surrogate Code Point. A Unicode code point in the range U+DC00 to U+DFFF. (See definition D73 in Section 3.8, Surrogates.)

Low-Surrogate Code Unit. A 16-bit code unit in the range DC00₁₆ to DFFF₁₆, used in UTF-16 as the trailing code unit of a surrogate pair. Also known as a trailing surrogate. (See definition D74 in Section 3.8, Surrogates.)

LSB. Acronym for least significant byte.

LZW. Acronym for Lempel-Ziv-Welch, a standard algorithm widely used for compression of data.

Majuscule. Synonym for uppercase. (See case.)

Mathematical Property. Informative property of characters that are used as operators in mathematical formulae.

Matra. A dependent vowel in an Indic script. It is the name for vowel letters that follow consonant letters in logical order. A matra often has a completely different letterform from that for the same phonological vowel used as an independent letter.

MBCS. Acronym for multibyte character set.

MCM. Acronym for modifier combining mark, a subset of combining marks used in the Arabic Mark Transient Reordering Algorithm. (See Unicode Standard Annex #53, “Unicode Arabic Mark Rendering.”)

MIME. Multipurpose Internet Mail Extensions. MIME is a standard that allows the embedding of arbitrary documents and other binary data of known types (images, sound, video, and so on) into e-mail handled by ordinary Internet electronic mail interchange protocols.

Minimal Well-Formed Code Unit Subsequence. A well-formed Unicode code unit sequence that maps to a single Unicode scalar value. (See definition D85a in Section 3.9, Unicode Encoding Forms.)

Minuscule. Synonym for lowercase. (See case.)

Mirrored Property. The property of characters whose images are mirrored horizontally in text that is laid out from right to left (versus from left to right). (See Section 4.7, Bidi Mirrored.)

Missing Glyph. (See replacement glyph.)

Modifier Letter. A character with the Lm General Category in the Unicode Character Database. Modifier letters, which look like letters or punctuation, modify the pronunciation of other letters (similar to diacritics). (See Section 7.8, Modifier Letters.)

Mongolian Free Variation Selector. A subset of variation selectors, encoded in the range U+180B..U+180D, which are used specifically for the definition of standardized variation sequences for the Mongolian script. A Mongolian free variation selector always takes a Mongolian letter as its base, but is otherwise not architecturally distinct from the general-purpose variation selectors. Commonly abbreviated FVS1, FVS2, and FVS3.

Mongolian Variation Sequence. A standardized variation sequence which has a Mongolian letter as its base character. All of the currently defined Mongolian variation sequences use the Mongolian free variation selectors in the range U+180B..U+180D, but no architectural constraint prevents such sequences from also using general-purpose variation selector characters in the range U+FE00..U+FE0D. Mongolian variation sequences are unusual in that many specify a positional context (for example, initial, medial, or final) for their use, as well as a particular glyph presentation.

Monotonic. Modern Greek written with the basic accent, the tonos.

Mora. A phonological term: the unit of sound which determines syllable weight in some languages. Some syllabaries have characteristics which reflect moraic structure more or less exactly. In particular, the Japanese kana syllabaries actually write one character per mora, rather than one character per syllable. The Vai syllabary also counts final nasals as distinct moras, and writes moras instead of syllables.

MSB. Acronym for most significant byte.

Multibyte Character Set. A character set encoded with a variable number of bytes per character, often abbreviated as MBCS. Many large character sets have been defined as MBCS so as to keep strict compatibility with the ASCII subset and/or ISO/IEC 2022.

Named Unicode Algorithm. A Unicode algorithm that is specified in the Unicode Standard or in other standards published by the Unicode Consortium and that is given an explicit name for ease of reference. (See definition D18 in Section 3.4, Characters and Encoding. See also Table 3-1, “Named Unicode Algorithms,” for a list of named Unicode algorithms.)

Namespace. (1) A set of names, no two of which are identical. (2) A set of names together with name matching rules, so that all names are distinct under the matching rules. (See definition D6 in Section 3.3, Semantics.) Character names are distinct if they do not match under the name matching rules in effect for the standard.

Nekudot. Marks that indicate vowels or other modifications of consonantal letters in Hebrew.

Neutral Character. A character that can be written either right to left or left to right, depending on context. (See Unicode Standard Annex #9, “Unicode Bidirectional Algorithm.”)

NFC. (See Normalization Form C.)

NFD. (See Normalization Form D.)

NFKC. (See Normalization Form KC.)

NFKD. (See Normalization Form KD.)

Noncharacter. A code point that is permanently reserved and that will never be assigned to an abstract character. Noncharacters consist of the values U+nFFFE and U+nFFFF (where n is from 0 to 10₁₆), and the values U+FDD0..U+FDEF. See the FAQ on Private-Use Characters, Noncharacters and Sentinels.

Non-joiner. An invisible character that affects the joining behavior of surrounding characters. (See Section 9.2, Arabic, and “Cursive Connection” in Section 23.2, Layout Controls.)

Non-overridable. A characteristic of a Unicode character property that cannot be changed by a higher-level protocol.

Nonspacing Diacritic. A diacritic that is a nonspacing mark.

Nonspacing Mark. A combining character with the General Category of Nonspacing Mark (Mn) or Enclosing Mark (Me). (See definition D53 in Section 3.6, Combination.) The position of a nonspacing mark in presentation depends on its base character. It generally does not consume space along the visual baseline in and of itself. (See also combining character.)

Non-starter Decomposition. A canonical decomposition mapping to a sequence of more than one character, for which the first character in that sequence is not a Starter. (Used in the definition of Unicode Normalization Forms.) (See definition D111 in Section 3.11, Normalization Forms.)

Normalization. A process of removing alternate representations of equivalent sequences from textual data, to convert the data into a form that can be binary-compared for equivalence. In the Unicode Standard, normalization refers specifically to processing to ensure that canonical-equivalent (and/or compatibility-equivalent) strings have unique representations. For more information, see “Equivalent Sequences” in Section 2.2, Unicode Design Principles, and Section 3.11, Normalization Forms.

Normalization Form. One of the four Unicode normalization forms defined in Section 3.11, Normalization Forms—namely, NFC, NFD, NFKC, and NFKD. For more information and examples, see Section 1.1, Canonical and Compatibility Equivalence in Unicode Standard Annex #15, "Unicode Normalization Forms."

Normalization Form C (NFC). A normalization form that erases any canonical differences, and generally produces a composed result. For example, a + umlaut is converted to ä in this form. This form most closely matches legacy usage. The formal definition is D120 in Section 3.11, Normalization Forms.

Normalization Form D (NFD). A normalization form that erases any canonical differences, and produces a decomposed result. For example, ä is converted to a + umlaut in this form. This form is most often used in internal processing, such as in collation. The formal definition is D118 in Section 3.11, Normalization Forms.

Normalization Form KC (NFKC). A normalization form that erases both canonical and compatibility differences, and generally produces a composed result: for example, the single ǆ character is converted to d + ž in this form. This form is commonly used in matching. The formal definition is D121 in Section 3.11, Normalization Forms.

Normalization Form KD (NFKD). A normalization form that erases both canonical and compatibility differences, and produces a decomposed result: for example, the single ǆ character is converted to d + z + caron in this form. The formal definition is D119 in Section 3.11, Normalization Forms.

Normative. Required for conformance with the Unicode Standard.

NSM. Acronym for nonspacing mark.

Numeric Value Property. A property of characters used to represent numbers. (See Section 4.6, Numeric Value.)

Obsolete. Applies to a character that is no longer in current use, but that has been used historically. Whether a character is obsolete depends on context: For example, the Cyrillic letter big yus is obsolete for Russian, but is used in modern Bulgarian. (Not the same as deprecated.)

Octet. An ordered sequence of eight bits considered as a unit. The Unicode Standard follows current industry practice in referring to an octet as a byte. (See byte.)

Orthographic Syllable. A two-dimensional visual arrangement of glyphs that forms a unit in Brahmic scripts. Also known as aksara. At the core of an orthographic syllable is a base character, which can be a consonant, an independent vowel, or (in some scripts) a numeric character, or a ligature formed from base characters and other characters. Attached to this core may be dependent forms (such as half-forms, subjoined forms, repha forms, medial forms) of consonants or independent vowels, as well as nukta marks, virama marks, dependent vowel marks, register shifter marks, tone marks, final consonant marks, and other marks. It is common for different components of orthographic syllables to form ligatures. Orthographic syllables often don’t correspond to phonological syllables; it is common for the final consonants of phonological syllables to become the base characters, or sometimes dependent forms, of subsequent orthographic syllables.

Out-of-Band. An out-of-band channel conveys additional information about text in such a way that the textual content, as encoded, is completely untouched and unmodified. This is typically done by separate data structures that point into the text.

Overridable. A characteristic of a Unicode character property that may be changed by a higher-level protocol to create desired implementation effects.

Oxia. Greek term for acute accent, used in polytonic Greek character names.

P-Q

Paragraph Direction. The default direction (left or right) of the text of a paragraph. This direction does not change the display order of characters within an Arabic or English word. However, it does change the display order of adjacent Arabic and English words, and the display order of neutral characters, such as punctuation and spaces. For more details, see Unicode Standard Annex #9, “Unicode Bidirectional Algorithm,” especially definitions BD2–BD5.

Paragraph Embedding Level. The embedding level that determines the default bidirectional orientation of the text in that paragraph.

Perispomeni. Greek term for circumflex accent, used in polytonic Greek character names.

Phoneme. A minimally distinct sound in the context of a particular spoken language. For example, in American English, /p/ and /b/ are distinct phonemes because pat and bat are distinct; however, the two different sounds of /t/ in tick and stick are not distinct in English, even though they are distinct in other languages such as Thai.

Pictograph (or pictogram). Any symbol that denotes an object by means of a more or less conventional visual likeness—for example, ✈. (See emoji, ideograph, logograph.)

Pinyin. Standard system for the romanization of Chinese on the basis of Mandarin pronunciation.

Pivot Conversion. The use of a third character encoding to serve as an intermediate step in the conversion between two other character encodings. The Unicode Standard is widely used to support pivot conversion, as its character repertoire is a superset of most other coded character sets.

Plain Text. Computer-encoded text that consists only of a sequence of code points from a given standard, with no other formatting or structural information. Plain text interchange is commonly used between computer systems that do not share higher-level protocols. (See also rich text.)

Plane. A range of 65,536 (10000₁₆) contiguous Unicode code points, where the first code point is an integer multiple of 65,536 (10000₁₆). Planes are numbered from 0 to 16, with the number being the first code point of the plane divided by 65,536. Thus Plane 0 is U+0000..U+FFFF, Plane 1 is U+10000..U+1FFFF, ..., and Plane 16 (10₁₆) is U+100000..10FFFF. (Note that ISO/IEC 10646 uses hexadecimal notation for the plane numbers—for example, Plane B instead of Plane 11). (See Basic Multilingual Plane and supplementary planes.)

Points. (1) The nonspacing vowels and other signs of written Hebrew. (2) A unit of measurement in typography.

Polytonic. Ancient Greek written with several contrastive accents.

Precomposed Character. (See decomposable character.)

Presentation Form. A ligature or variant glyph that has been encoded as a character for compatibility. (See also compatibility character (1).)

Primary Composite. A Canonical Decomposable Character which is not a Full Composition Exclusion. (Used in the definition of Unicode Normalization Forms.) (See definition D114 in Section 3.11, Normalization Forms.)

Private Use. Refers to designated code points in the Unicode Standard or other character encoding standards whose interpretations are not specified in those standards and whose use may be determined by private agreement among cooperating users.

Private Use Area (PUA). Any one of the three blocks of private-use code points in the Unicode Standard.

Private-Use Character. A character that has been assigned to a Private-use code point by private agreement.

Private-Use Code Point. Code points in the ranges U+E000..U+F8FF, U+F0000..U+FFFFD, and U+100000..U+10FFFD. (See definition D49 in Section 3.5, Properties.) These code points are designated in the Unicode Standard for private use.

Productive. Said of a feature or rule that can be employed in novel combinations or circumstances, rather than being restricted to a fixed list. In the Unicode Standard, combining marks—particularly the accents—are productive. In contrast, variation selectors are deliberately not productive. Also known as generative.

Property. (See character properties.)

Property Alias. A unique identifier for a particular Unicode character property. (See definition D47 in Section 3.5, Properties.)

Property Value Alias. A unique identifier for a particular enumerated value for a particular Unicode character property. (See definition D48 in Section 3.5, Properties.)

Prosgegrammeni. Greek term for adscript iota, used in polytonic Greek character names.

Provisional. A property or feature that is unapproved and tentative, and that may be incomplete or otherwise not in a usable state.

Psili. Greek term for smooth breathing mark, used in polytonic Greek character names.

PUA. Acronym for Private Use Area.

Puḷḷi. The Tamil name for virama. (See virama.)

Punycode. Punycode is an algorithm, defined in RFC 3492, that compactly represents Unicode strings using 7-bit ASCII, while leaving the ASCII characters unmapped. Punycode strings can be identified by their characteristic prefix "xn--". Punycode is used to transform IDNs to an ASCII-compatible form.

Radical. A structural component of a Han character conventionally used for indexing. The traditional number of such radicals is 214.

Rendering. (1) The process of selecting and laying out glyphs for the purpose of depicting characters. (2) The process of making glyphs visible on a display device.

Repertoire. (See character repertoire.)

Replacement Character. A character used as a substitute for an uninterpretable character from another encoding. The Unicode Standard uses U+FFFD replacement character for this function.

Replacement Glyph. A glyph used to render a character that cannot be rendered with the correct appearance in a particular font. It often is shown as an open or black rectangle. Also known as a missing glyph. (See Section 5.3, Unknown and Missing Characters.)

Reorderable Pair. Two adjacent characters A and B in a coded character sequence <A, B> are a Reorderable Pair if and only if ccc(A) > ccc(B) > 0. (Used in the definition of Unicode Normalization Forms.) (See definition D108 in Section 3.11, Normalization Forms.)

Reserved Code Point. Any code point of the Unicode Standard that is reserved for future assignment. Also known as an unassigned code point. (See definition D15 in Section 3.4, Characters and Encoding, and Section 2.4, Code Points and Characters.)

RGI. Acronym for Recommended for General Interchange. This is a term used in Unicode Technical Standard #51, "Unicode Emoji", to refer to a subset of a larger set of emoji (or emoji sequences) that is intended to be widely supported across multiple platforms. See use of RGI.

Rich Text. Also known as styled text. The result of adding information to plain text. Examples of information that can be added include font data, color, formatting information, phonetic annotations, interlinear text, and so on. The Unicode Standard does not address the representation of rich text. It is expected that systems and applications will implement proprietary forms of rich text. Some public forms of rich text are available (for example, ODA, HTML, and SGML). When everything except primary content is removed from rich text, only plain text should remain.

Romaji (ローマ字). The Japanese name for Roman characters, that is, the Latin script. Latin characters are fairly commonly interspersed in the Japanese writing system, whether as single letters, or for complete words, acronyms, or abbreviations borrowed from other languages. (See also kanji and kana.)

Row. A range of 256 contiguous Unicode code points, where the first code point is an integer multiple of 256. Two code points are in the same row if they share all but the last two hexadecimal digits. (See plane.)

SAM. Acronym for Syriac abbreviation mark.

SBCS. Acronym for single-byte character set. Any one-byte character encoding. This term is generally used in contrast with DBCS and/or MBCS.

Scalar Value. (See Unicode scalar value.)

Script. A collection of letters and other written signs used to represent textual information in one or more writing systems. For example, Russian is written with a subset of the Cyrillic script; Ukrainian is written with a different subset. The Japanese writing system uses several scripts.

Script Code. An identifier referring to a specific script. ISO 15924, “Codes for the representation of names of scripts,” is the ISO registration standard which specifies the framework for both alphanumeric and numeric codes for script names. For example "Cher" is the alphanumeric script code for the Cherokee script, and 445 is the corresponding numeric script code. The Unicode Consortium is the registration authority and maintains the ISO 15924 code lists.

Script Designator. The part of a character name (or block name), usually at the beginning of that name, which generally identifies the script of the character (or that of most characters in the block). For example, the substring "LATIN" in the character name "LATIN SMALL LETTER S" is a script designator. Note that not all character names and block names have script designators. The Script property in the UCD should be used instead to determine the script of any particular character. (See Unicode Standard Annex #24, Unicode Script Property.)

Scriptio Continua. A writing style without spaces or punctuation.

Script Property. 1. An enumerated character property that assigns every Unicode character a particular Script property value. See Unicode Standard Annex #24, “Unicode Script Property.” 2. Informally, the term script property also refers to characteristics of the script as a whole, in such phrasings as, “Arabic is a right-to-left script,” or “Lydian is an historic script.”

SCSU. Acronym for Standard Compression Scheme for Unicode. See Unicode Technical Standard #6, “A Standard Compression Scheme for Unicode.”

Semi-Stable Comparison. (See deterministic comparison.)

SGML. Standard Generalized Markup Language. A standard framework, defined in ISO 8879, for defining particular text markup languages. The SGML framework allows for mixing structural tags that describe format with the plain text content of documents, so that fancy text can be fully described in a plain text stream of data. (See also HTML, XML, and rich text.)

Shaping Characters. Characters that assume different glyphic forms depending on the context.

Shift-JIS. A shifted encoding of the Japanese character encoding standard, JIS X 0208, widely deployed in PCs.

Signature. An optional code sequence at the beginning of a stream of coded characters that identifies the character encoding scheme used for the following text. (See Unicode signature.)

Singleton Decomposition. A canonical decomposition mapping from a character to a different single character. (Used in the definition of Unicode Normalization Forms.) (See definition D110 in Section 3.11, Normalization Forms.)

Sinogram. A technical term for a Chinese character. In the Unicode Standard, sinograms are systematically referred to instead as CJK ideographs or Han ideographs. (See ideograph.)

SI Unit. A unit of the International System of Units, the modern form of the metric system. This consists of the system of base units, such as the second, meter, and kilogram, a set of derived units, such as newton, joule, and volt, and a set of modifying prefixes, such as milli-, nano-, pico-, mega-, giga-, tera-, and so forth.

SJIS. Acronym for Shift-JIS.

Small Letter. Synonym for lowercase letter. (See case.)

Sorting. (See collation.)

Spacing Mark. A combining character that is not a nonspacing mark. (See definition D55 in Section 3.6, Combination.) (See nonspacing mark.)

Stable Comparison. (See deterministic comparison.)

Stable Sort. A sort in which two records with a field that compares as equal will retain their relative order if sorted according to that field. This is a property of the sorting algorithm, and not of the comparison mechanism. For example, a bubble sort is stable, whereas a Quicksort is not.

Standard Korean Syllable Block. (See Korean syllable block.)

Standardized Variation Sequence. A variation sequence defined in the UCD data file StandardizedVariants.txt. A standardized variation sequence cannot have an ideographic character as its base, and it makes use of a variation selector in the range U+FE00..U+FE0F or U+180B..U+180D. Note that U+FE0E and U+FE0F are reserved for special functions when applied to emoji base characters. See Unicode Technical Standard #51, "Unicode Emoji." The term standardized variation sequence is sometimes abbreviated as "SVS".

Starter. Any code point (assigned or not) with combining class of zero (ccc=0). (Used in the definition of Unicode Normalization Forms.) (See definition D107 in Section 3.11, Normalization Forms.)

Static Form. (See decomposable character.)

Styled Text. (See rich text.)

Subtending Mark. A format character whose graphic form extends under a sequence of following characters—for example, U+0600 arabic number sign.

Supplementary Character. A Unicode encoded character having a supplementary code point.

Supplementary Code Point. A Unicode code point between U+10000 and U+10FFFF.

Supplementary Planes. Planes 1 through 16, consisting of the supplementary code points.

Surrogate Character. A misnomer. It would be an encoded character having a surrogate code point, which is impossible. Do not use this term.

Surrogate Code Point. A Unicode code point in the range U+D800..U+DFFF. Reserved for use by UTF-16, where a pair of surrogate code units (a high surrogate followed by a low surrogate) “stand in” for a supplementary code point.

Surrogate Pair. A representation for a single abstract character that consists of a sequence of two 16-bit code units, where the first value of the pair is a high-surrogate code unit, and the second is a low-surrogate code unit. (See definition D75 in Section 3.8, Surrogates.)

Syllabary. A type of writing system in which each symbol typically represents both a consonant and a vowel, or in some instances more than one consonant and a vowel.

Syllable. (1) An element of a syllabary. (2) A basic unit of articulation that corresponds to a pulmonary pulse.

Syllable Block. A sequence of Korean characters that should be grouped into a single square cell for display. (See Section 3.12, Conjoining Jamo Behavior.)

Symmetric Swapping. The process of rendering a character with a mirrored glyph when its resolved directionality is right-to-left in a bidirectional context. (See mirrored property and Unicode Standard Annex #9, “Unicode Bidirectional Algorithm.”)

Tagging. The association of attributes of text with a point or range of the primary text. The value of a particular tag is not generally considered to be a part of the “content” of the text. A typical example of tagging is to mark the language or the font for a portion of text.

Tailorable. A characteristic of an algorithm for which a higher-level protocol may specify different results than those specified in the algorithm. A tailorable algorithm without actual tailoring is also known as a default algorithm, and the results of an algorithm without tailoring are known as the default results.

Tanwin. Marks used in the Arabic script to indicate vocalization with long vowels or postnasalization. A subtype of tashkil.

Tashkil. Marks used in the Arabic script to indicate vocalization of text, as well as other types of phonetic guides to correct pronunciation. A basic Arabic letter plus any of these types of marks is not encoded as a single, precomposed character, and should always be represented as a sequence of letter plus combining mark. Contrast ijam. See also harakat, tanwin, and Section 9.2, Arabic.

TES. Acronym for transfer encoding syntax.

TeX. Computer language designed for use in typesetting—in particular, for typesetting math and other technical material. (According to Donald Knuth, TeX rhymes with the word blecchhh.)

Text Element. A minimum unit of text in relation to a particular text process, in the context of a given writing system. In general, the mapping between text elements and code points is many-to-many. (See Chapter 2, General Structure.)

Titlecase. Uppercased initial letter followed by lowercase letters in words. A casing convention often used in titles, headers, and entries, as exemplified in this glossary.

Titlo Letter. A superscripted letter (written above) used in Old Church Slavonic text.

TLD. Acronym for top-level domain.

Tonal Sandhi. A phonological process whereby the tone associated with one syllable in a tonal language influences the realization of a tone associated with a neighboring syllable.

Tone Mark. A diacritic or nonspacing mark that represents a phonemic tone. Tone languages are common in Southeast Asia and Africa. Because tones always accompany vowels (the syllabic nucleus), they are most frequently written using functionally independent marks attached to a vowel symbol. However, some writing systems such as Thai place tone marks on consonant symbols; Chinese does not use tone marks (except when it is written phonemically).

Tonemic. Refers to the underlying, distinctive units of a tonal system in a language. Tones of a tonal language are often referred to by numbers (“tone 1,” “tone 2,” and so on), and each tone has an idealized, specific tone level or contour that is considered to be its tonemic value. The term was created by analogy with phonemic.

Tonetic. Refers to the surface, actual pitch realization of tones in a tonal system. Tonetic values are what can be directly measured by tracking pitch contours in actual speech recordings. The term was created by analogy with phonetic.

Tonos. The basic accent in modern Greek, having the form of an acute accent.

Top-Level Domain. The first-level set of domain names, consisting of generic top-level domains such as .com, .edu, .org, and .gov, and country code top-level domains such as .jp, .cn, .de, and so forth. Often abbreviated as TLD.

Trailing Consonant. (1) In Korean, a jamo character with the Hangul_Syllable_Type property value Trailing_Jamo (in the range U+11A8..U+11F9). Abbreviated as T. (See definition D128 in Section 3.12, Conjoining Jamo Behavior.) (2) Any final consonant in a syllable.

Trailing Surrogate. Synonym for low-surrogate code unit.

Transcoding. Conversion of character data between different character sets.

Transfer Encoding Syntax. A reversible transformation applied to text and other data to allow it to be transmitted—for example, Base64, uuencode.

Transformation Format. A mapping from a coded character sequence to a unique sequence of code units (typically bytes).

Triangulation. (See pivot conversion.)

Typographic Interaction. Graphical application of one nonspacing mark in a position relative to a grapheme base that is already occupied by another nonspacing mark, so that some rendering adjustment must be done (such as default stacking or side-by-side placement) to avoid illegible overprinting or crashing of glyphs. (See definition D106 in Section 3.11, Normalization Forms.)

UAX. Acronym for Unicode Standard Annex.

UBA. Acronym for Unicode Bidirectional Algorithm.

UCA. Acronym for Unicode Collation Algorithm.

UCD. Acronym for Unicode Character Database. (See Section 4.1, Unicode Character Database.)

UCS. Acronym for Universal Character Set, which is specified by International Standard ISO/IEC 10646, which is equivalent in repertoire to the Unicode Standard.

UCS-2. ISO/IEC 10646 encoding form: Universal Character Set coded in 2 octets, limited to the Basic Multilingual Plane. (See Appendix C, Relationship to ISO/IEC 10646.)

UCS-4. ISO/IEC 10646 encoding form: Universal Character Set coded in 4 octets. (See Appendix C, Relationship to ISO/IEC 10646.)

Umlaut. Two horizontal dots over a letter, as in German Köpfe. The umlaut is not distinguished from the diaeresis in the Unicode character encoding. (See diaeresis.)

Unassigned Character. A code point that is not assigned to an abstract character. This refers to surrogate code points, noncharacters, and reserved code points. (See Section 2.4, Code Points and Characters.)

Unassigned Code Point. Synonym for reserved code point.

Undesignated Code Point. Synonym for reserved code point.

Unicameral. A script that has no case distinctions. Most often used in the context of European alphabets.

Unicode. (1) The standard for digital representation of the characters used in writing all of the world's languages. Unicode provides a uniform means for storing, searching, and interchanging text in any language. It is used by all modern computers and is the foundation for processing text on the Internet. Unicode is developed and maintained by the Unicode Consortium: https://www.unicode.org. (2) A label applied to software internationalization and localization standards developed and maintained by the Unicode Consortium.

Unicode Algorithm. The logical description of a process used to achieve a specified result involving Unicode characters. (See definition D17 in Section 3.4, Characters and Encoding.)

Unicode Bidirectional Algorithm. The algorithm that specifies the positioning of characters in bidirectional text containing characters that display from right to left, such as in Arabic or Hebrew. See Unicode Standard Annex #9, “Unicode Bidirectional Algorithm.”

Unicode Character Database. A collection of files providing normative and informative Unicode character properties and mappings. (See Chapter 4, Character Properties, and the Unicode Character Database.)

Unicode Collation Algorithm. Tailorable text comparison mechanism used for searching, sorting, and matching Unicode strings. See Unicode Technical Standard #10, “Unicode Collation Algorithm.”

Unicode Common Locale Data Repository. The repository of locale data in XML format maintained by the Unicode Consortium (https://cldr.unicode.org). This repository provides information needed in the localization of software products into a wide variety of languages, supplying (among other things): date, time, number, and currency formats; sorting, searching, and matching information; and translated names for languages, territories, scripts, currencies, and time zones. (See also Unicode Locale Data Markup Language.)

Unicode Consortium. A standards development organization creating widely-used specifications related to character encoding, as well as for software internationalization and localization. Major projects are the Unicode Standard and the Unicode Locales Project, which defines repositories of standardized data needed to develop software for particular regions and cultures. The Consortium was founded in 1991, and is headquartered in Mountain View, California. Its current members include major software corporations, governments, and academic institutions. See https://www.unicode.org.

Unicode Encoding Form. A character encoding form that assigns each Unicode scalar value to a unique code unit sequence. The Unicode Standard defines three standard Unicode encoding forms: UTF-8, UTF-16, and UTF-32. (See definition D79 in Section 3.9, Unicode Encoding Forms.)

Unicode Encoding Scheme. A specified byte serialization for a Unicode encoding form, including the specification of the handling of a byte order mark (BOM), if allowed. (See definition D94 in Section 3.10, Unicode Encoding Schemes.)

Unicode Locale Data Markup Language. The XML specification for the exchange of locale data, defined by Unicode Technical Standard #35, "Unicode Locale Data Markup Language (LDML)." (See also Unicode Common Locale Data Repository.)

Unicode Scalar Value. Any Unicode code point except high-surrogate and low-surrogate code points. In other words, the ranges of integers 0 to D7FF₁₆ and E000₁₆ to 10FFFF₁₆ inclusive. (See definition D76 in Section 3.9, Unicode Encoding Forms.)

Unicode Signature. An implicit marker to identify a file as containing Unicode text in a particular encoding form. An initial byte order mark (BOM) may be used as a Unicode signature.

Unicode Standard Annex. An integral part of the Unicode Standard published as a separate document.

Unicode String. A code unit sequence containing code units of a particular Unicode encoding form (whether well-formed or not). (See definition D80 in Section 3.9, Unicode Encoding Forms.)

Unicode Technical Note. Informative publication containing information of possible interest concerning the Unicode Standard or related topics.

Unicode Technical Report. Formally approved Unicode Consortium publication containing informative technical analysis of a topic related to the Unicode Standard.

Unicode Technical Standard. Formally approved specification published by the Unicode Consortium that is related to, but not part of, the Unicode Standard.

Unicode Transformation Format. An ambiguous synonym for either Unicode encoding form or Unicode encoding scheme. The latter terms are now preferred.

Unification. The process of identifying characters that are in common among writing systems.

Unihan. (1) The concept of unification of the encoding of CJK ideographs across multiple, distinct legacy East Asian character encoding standards. (2) Short for the Unicode Han Database. (See Unicode Standard Annex #38, “Unicode Han Database (Unihan).”)

Unikemet. Short for the Unicode Egyptian Hieroglyph Database, a datafile containing source references and other extensive information about the hieroglyphs. (See Unicode Standard Annex #57, “Unicode Egyptian Hieroglyph Database (Unikemet).”)

UPA. Acronym for Uralic Phonetic Alphabet.

Uppercase. (See case.)

URO. Acronym for Unified Repertoire and Ordering, the original set of CJK unified ideographs used in the Unicode Standard.

User-Defined Character. (See EUDC.)

User-Perceived Character. What everyone thinks of as a character in their script.

UTF. Acronym for Unicode (or UCS) Transformation Format.

UTF-2. Obsolete name for UTF-8.

UTF-7. Unicode (or UCS) Transformation Format, 7-bit encoding form, specified by RFC 2152.

UTF-8. A multibyte encoding for text that represents each Unicode character with 1 to 4 bytes, and which is backward-compatible with ASCII. UTF-8 is the predominant form of Unicode in web pages. More technically: (1) The UTF-8 encoding form. (2) The UTF-8 encoding scheme. (3) “UCS Transformation Format 8,” defined in Annex D of ISO/IEC 10646:2003, technically equivalent to the definitions in the Unicode Standard.

UTF-8 Encoding Form. The Unicode encoding form that assigns each Unicode scalar value to an unsigned byte sequence of one to four bytes in length, as specified in Table 3-6, "UTF-8 Bit Distribution." (See definition D92 in Section 3.9, Unicode Encoding Forms.)

UTF-8 Encoding Scheme. The Unicode encoding scheme that serializes a UTF-8 code unit sequence in exactly the same order as the code unit sequence itself. (See definition D95 in Section 3.10, Unicode Encoding Schemes.)

UTF-16. A multibyte encoding for text that represents each Unicode character with 2 or 4 bytes; it is not backward-compatible with ASCII. It is the internal form of Unicode in many programming languages, such as Java, C#, and JavaScript, and in many operating systems. More technically: (1) The UTF-16 encoding form. (2) The UTF-16 encoding scheme. (3) “Transformation format for 16 planes of Group 00,” defined in Annex C of ISO/IEC 10646:2003; technically equivalent to the definitions in the Unicode Standard.

UTF-16 Encoding Form. The Unicode encoding form that assigns each Unicode scalar value in the ranges U+0000..U+D7FF and U+E000..U+FFFF to a single unsigned 16-bit code unit with the same numeric value as the Unicode scalar value, and that assigns each Unicode scalar value in the range U+10000..U+10FFFF to a surrogate pair, according to Table 3-5, “UTF-16 Bit Distribution.” (See definition D91 in Section 3.9, Unicode Encoding Forms.)

UTF-16 Encoding Scheme. The UTF-16 encoding scheme that serializes a UTF-16 code unit sequence as a byte sequence in either big-endian or little-endian formats. (See definition D98 in Section 3.10, Unicode Encoding Schemes.)

UTF-16BE. The Unicode encoding scheme that serializes a UTF-16 code unit sequence as a byte sequence in big-endian format. (See definition D96 in Section 3.10, Unicode Encoding Schemes.)

UTF-16LE. The Unicode encoding scheme that serializes a UTF-16 code unit sequence as a byte sequence in little-endian format. (See definition D97 in Section 3.10, Unicode Encoding Schemes.)

UTF-32. A multibyte encoding for text that represents each Unicode character with 4 bytes; it is not backward-compatible with ASCII. More technically: (1) The UTF-32 encoding form. (2) The UTF-32 encoding scheme.

UTF-32 Encoding Form. The Unicode encoding form that assigns each Unicode scalar value to a single unsigned 32-bit code unit with the same numeric value as the Unicode scalar value. (See definition D90 in Section 3.9, Unicode Encoding Forms.)

UTF-32 Encoding Scheme. The Unicode encoding scheme that serializes a UTF-32 code unit sequence as a byte sequence in either big-endian or little-endian formats. (See definition D101 in Section 3.10, Unicode Encoding Schemes.)

UTF-32BE. The Unicode encoding scheme that serializes a UTF-32 code unit sequence as a byte sequence in big-endian format. (See definition D99 in Section 3.10, Unicode Encoding Schemes.)

UTF-32LE. The Unicode encoding scheme that serializes a UTF-32 code unit sequence as a byte sequence in little-endian format. (See definition D100 in Section 3.10, Unicode Encoding Schemes.)

UTN. Acronym for Unicode Technical Note.

UTR. Acronym for Unicode Technical Report.

UTS. Acronym for Unicode Technical Standard.

Varia. Greek term for grave accent, used in polytonic Greek character names.

Variation Selector. Any of three ranges of Unicode characters designated for use in defining a variation sequence. Variation selectors in the range U+FE00..U+FE0F are known as general-use variation selectors and are used for standardized variation sequences. Two of these, U+FE0E and U+FE0F, have specialized functions when used with emoji base characters. Variation selectors in the range U+180B..U+180D are known as Mongolian Free Variation Selector; their use is limited to standardized variation sequences for the Mongolian script. Variation selectors in the range U+E0100..U+E01EF are known as ideographic variation selectors and are used for ideographic variation sequences. Variation selectors are all nonspacing combing marks (General_Category=Mn). They have no graphic shape of their own; instead they function to pick out a particular, defined subset of potential graphic presentations for the base character to which they are applied. All variation selectors are default ignorable code points (DICP=Yes), meaning that if they are not interpretable in combination with their base character, they should be ignored for display, rather than shown with a nondisplayable glyph box, for example. See Section 23.4, Variation Selectors. The term variation selector is sometimes abbreviated as "VS".

Variation Sequence. A sequence consisting of precisely two code points: a base character (or a spacing mark [gc=Mc]) followed by a single variation selector. The two-character sequence is referred to as a variant of the base character or spacing mark. The function of the variation sequence is to pick out a particular, defined subset of potential graphic presentations of the base character (or spacing mark). Not all potential combinations of base characters and variation selectors have interpretations. Only the following variation sequences have valid interpretations: a standardized variation sequence, a registered ideographic variation sequence, and a variation sequence with an emoji base character defined in the data files associated with Unicode Technical Standard #51, "Unicode Emoji".

Virama. From Sanskrit. The name of a sign used in many Indic and other Brahmi-derived scripts to suppress (or "kill") the inherent vowel of the consonant to which it is applied, thereby generating a dead consonant. (See Section 12.1, Devanagari.) The sign varies in shape from script to script, and may be known by other names in various languages. For example, in Hindi it is known as hal or halant, in Bangla it is called hasant, and in Tamil it is called pulli. The Unicode Standard uses the term virama in three specialized senses:

For a visible mark which suppresses the inherent vowel of the consonant to which it is applied. This corresponds to characters with Indic_Syllabic_Category=Pure_Killer.
For invisible formatting characters that create the conjunct form of a subsequent or preceding consonant or independent vowel, or of the preceding or subsequent consonants combined. This corresponds to characters with Indic_Syllabic_Category=Invisible_Stacker.
For characters that can act either as a Pure_Killer or an Invisible_Stacker at the discretion of the font engineer. This corresponds to characters with Indic_Syllabic_Category=Virama.

Visual Ambiguity. A situation arising from two characters (or sequences of characters) being rendered indistinguishably.

Visual Order. Characters ordered as they are presented for reading. (Contrast with logical order.)

Vocalization. Marks placed above, below, or within consonants to indicate vowels or other aspects of pronunciation. A feature of Middle Eastern scripts.

Vowel. 1. In phonetics, a sound characterized by open articulation, whose quality is then dependent on the shape of the vocal tract and the resulting harmonics in the sound wave. 2. In writing systems such as alphabets, a character used to represent a vowel sound. 3. Specifically in Korean, a jamo character with the Hangul_Syllable_Type property value Vowel_Jamo (in the range U+1161..U+11A2 or U+1160 hangul jungseong filler). Abbreviated as V. (See definition D125 in Section 3.12, Conjoining Jamo Behavior.)

Vowel Mark. In many scripts, a mark used to indicate a vowel or vowel quality.

Vowel Sign. A combining mark representing a dependent vowel, attached to a base character that usually represents a consonant. The term vowel sign is usually applicable in discussion of abugida writing systems. For Indic writing systems, in particular, vowel sign is often used as a synonym for matra.

Vrachy. Greek term for breve accent, used in polytonic Greek character names.

W3C. Acronym for World Wide Web Consortium.

wchar_t. The ANSI C defined wide character type, usually implemented as either 16 or 32 bits. ANSI specifies that wchar_t be an integral type and that the C language source character set be mappable by simple extension (zero- or sign-extension).

Well-Formed Code Unit Sequence. A code unit sequence that follows the specification of a Unicode encoding form. (See definition D85 in Section 3.9, Unicode Encoding Forms.)

Writing Direction. The direction or orientation of writing characters within lines of text in a writing system. Three directions are common in modern writing systems: left to right, right to left, and top to bottom.

Writing System. A set of rules for using one or more scripts to write a particular language. Examples include the American English writing system, the British English writing system, the French writing system, and the Japanese writing system.

X-Y

XML. eXtensible Markup Language. A subset of SGML constituting a particular text markup language for interchange of structured data. The Unicode Standard is the reference character set for XML content. (See also SGML and rich text.) XML is a trademark of the World Wide Web Consortium.

Ypogegrammeni. Greek term for subscript iota, used in polytonic Greek character names.

Y-variant. Two CJK unified ideographs with identical semantics and non-unifiable shapes, for example, U+732B and U+8C93. (See Z-variant.)

Z-variant. Two CJK unified ideographs with identical semantics and unifiable shapes, for example, U+8AAA and U+8AAC. (See Y-variant.)

Zenkaku. (See fullwidth.)

Zero Width. Characteristic of some spaces or format control characters that do not advance text along the horizontal baseline. (See nonspacing mark.)