diff --git a/UPGRADE-5.3.md b/UPGRADE-5.3.md
new file mode 100644
index 0000000000000..c7b1ef71bbde8
--- /dev/null
+++ b/UPGRADE-5.3.md
@@ -0,0 +1,9 @@
+UPGRADE FROM 5.2 to 5.3
+=======================
+
+HttpKernel
+----------
+
+ * Deprecated the `Kernel::$environment` property, use `Kernel::$mode` instead
+ * Deprecated the `KernelInterface::getEnvironment()` method, use `KernelInterface::getMode()` instead
+ * Deprecated the `ConfigDataCollector::getEnv()` method, use `ConfigDataCollector::getMode()` instead
diff --git a/UPGRADE-6.0.md b/UPGRADE-6.0.md
index 69db8ccddbb48..99b979ce92aa8 100644
--- a/UPGRADE-6.0.md
+++ b/UPGRADE-6.0.md
@@ -71,6 +71,9 @@ HttpKernel
 
  * Made `WarmableInterface::warmUp()` return a list of classes or files to preload on PHP 7.4+
  * Removed support for `service:action` syntax to reference controllers. Use `serviceOrFqcn::method` instead.
+ * Removed the `Kernel::$environment` property, use `Kernel::$mode` instead
+ * Removed the `KernelInterface::getEnvironment()` method, use `KernelInterface::getMode()` instead
+ * Removed the `ConfigDataCollector::getEnv()` method, use `ConfigDataCollector::getMode()` instead
 
 Inflector
 ---------
diff --git a/src/Symfony/Bridge/Twig/AppVariable.php b/src/Symfony/Bridge/Twig/AppVariable.php
index f5a6494ed29bc..89408bf48ecbe 100644
--- a/src/Symfony/Bridge/Twig/AppVariable.php
+++ b/src/Symfony/Bridge/Twig/AppVariable.php
@@ -27,6 +27,7 @@ class AppVariable
     private $tokenStorage;
     private $requestStack;
     private $environment;
+    private $mode;
     private $debug;
 
     public function setTokenStorage(TokenStorageInterface $tokenStorage)
@@ -44,6 +45,11 @@ public function setEnvironment(string $environment)
         $this->environment = $environment;
     }
 
+    public function setMode(string $mode): void
+    {
+        $this->mode = $mode;
+    }
+
     public function setDebug(bool $debug)
     {
         $this->debug = $debug;
@@ -130,6 +136,18 @@ public function getEnvironment()
         return $this->environment;
     }
 
+    /**
+     * Returns the current app mode name (e.g 'dev').
+     */
+    public function getMode(): string
+    {
+        if (null === $this->mode) {
+            throw new \RuntimeException('The "app.mode" variable is not available.');
+        }
+
+        return $this->mode;
+    }
+
     /**
      * Returns the current app debug mode.
      *
diff --git a/src/Symfony/Bridge/Twig/Tests/AppVariableTest.php b/src/Symfony/Bridge/Twig/Tests/AppVariableTest.php
index 59539f278c05a..599fe32db7b4f 100644
--- a/src/Symfony/Bridge/Twig/Tests/AppVariableTest.php
+++ b/src/Symfony/Bridge/Twig/Tests/AppVariableTest.php
@@ -45,6 +45,13 @@ public function testEnvironment()
         $this->assertEquals('dev', $this->appVariable->getEnvironment());
     }
 
+    public function testMode()
+    {
+        $this->appVariable->setMode('dev');
+
+        $this->assertEquals('dev', $this->appVariable->getMode());
+    }
+
     /**
      * @runInSeparateProcess
      */
@@ -120,6 +127,12 @@ public function testEnvironmentNotSet()
         $this->appVariable->getEnvironment();
     }
 
+    public function testModeNotSet()
+    {
+        $this->expectException('RuntimeException');
+        $this->appVariable->getMode();
+    }
+
     public function testDebugNotSet()
     {
         $this->expectException('RuntimeException');
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/AboutCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/AboutCommand.php
index e39772edf4db1..ca6a10821162a 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/AboutCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/AboutCommand.php
@@ -78,7 +78,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             ['<info>Kernel</>'],
             new TableSeparator(),
             ['Type', \get_class($kernel)],
-            ['Environment', $kernel->getEnvironment()],
+            ['Mode', $kernel->getMode()],
             ['Debug', $kernel->isDebug() ? 'true' : 'false'],
             ['Charset', $kernel->getCharset()],
             ['Cache directory', self::formatPath($kernel->getCacheDir(), $kernel->getProjectDir()).' (<comment>'.self::formatFileSize($kernel->getCacheDir()).'</>)'],
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php
index 0dada3d7d172f..bef1f416c46e1 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php
@@ -60,11 +60,11 @@ protected function configure()
             ])
             ->setDescription('Clears the cache')
             ->setHelp(<<<'EOF'
-The <info>%command.name%</info> command clears the application cache for a given environment
+The <info>%command.name%</info> command clears the application cache for a given mode
 and debug mode:
 
-  <info>php %command.full_name% --env=dev</info>
-  <info>php %command.full_name% --env=prod --no-debug</info>
+  <info>php %command.full_name% --mode=dev</info>
+  <info>php %command.full_name% --mode=prod --no-debug</info>
 EOF
             )
         ;
@@ -94,9 +94,8 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             throw new RuntimeException(sprintf('Unable to write in the "%s" directory.', $realCacheDir));
         }
 
-        $io->comment(sprintf('Clearing the cache for the <info>%s</info> environment with debug <info>%s</info>', $kernel->getEnvironment(), var_export($kernel->isDebug(), true)));
+        $io->comment(sprintf('Clearing the cache for the <info>%s</info> mode with debug <info>%s</info>', $kernel->getMode(), var_export($kernel->isDebug(), true)));
         $this->cacheClearer->clear($realBuildDir);
-        $this->cacheClearer->clear($realCacheDir);
 
         // The current event dispatcher is stale, let's not use it anymore
         $this->getApplication()->setDispatcher(new EventDispatcher());
@@ -199,7 +198,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             $io->comment('Finished');
         }
 
-        $io->success(sprintf('Cache for the "%s" environment (debug=%s) was successfully cleared.', $kernel->getEnvironment(), var_export($kernel->isDebug(), true)));
+        $io->success(sprintf('Cache for the "%s" mode (debug=%s) was successfully cleared.', $kernel->getMode(), var_export($kernel->isDebug(), true)));
 
         return 0;
     }
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/CacheWarmupCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/CacheWarmupCommand.php
index 8feb2dd9c51b2..fb6d9499f65df 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/CacheWarmupCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/CacheWarmupCommand.php
@@ -72,7 +72,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         $io = new SymfonyStyle($input, $output);
 
         $kernel = $this->getApplication()->getKernel();
-        $io->comment(sprintf('Warming up the cache for the <info>%s</info> environment with debug <info>%s</info>', $kernel->getEnvironment(), var_export($kernel->isDebug(), true)));
+        $io->comment(sprintf('Warming up the cache for the <info>%s</info> mode with debug <info>%s</info>', $kernel->getMode(), var_export($kernel->isDebug(), true)));
 
         if (!$input->getOption('no-optional-warmers')) {
             $this->cacheWarmer->enableOptionalWarmers();
@@ -84,7 +84,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             Preloader::append($preloadFile, $preload);
         }
 
-        $io->success(sprintf('Cache for the "%s" environment (debug=%s) was successfully warmed.', $kernel->getEnvironment(), var_export($kernel->isDebug(), true)));
+        $io->success(sprintf('Cache for the "%s" mode (debug=%s) was successfully warmed.', $kernel->getMode(), var_export($kernel->isDebug(), true)));
 
         return 0;
     }
diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/ContainerDebugCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/ContainerDebugCommand.php
index 7c330dbdf4f85..fd0b48c506ed5 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/ContainerDebugCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/ContainerDebugCommand.php
@@ -85,7 +85,7 @@ protected function configure()
 
 Display a specific environment variable by specifying its name with the <info>--env-var</info> option:
 
-  <info>php %command.full_name% --env-var=APP_ENV</info>
+  <info>php %command.full_name% --env-var=APP_MODE</info>
 
 Use the --tags option to display tagged <comment>public</comment> services grouped by tag:
 
diff --git a/src/Symfony/Bundle/FrameworkBundle/Console/Application.php b/src/Symfony/Bundle/FrameworkBundle/Console/Application.php
index d1a4682b50ab5..ae448436417bb 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Console/Application.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Console/Application.php
@@ -40,7 +40,8 @@ public function __construct(KernelInterface $kernel)
         parent::__construct('Symfony', Kernel::VERSION);
 
         $inputDefinition = $this->getDefinition();
-        $inputDefinition->addOption(new InputOption('--env', '-e', InputOption::VALUE_REQUIRED, 'The Environment name.', $kernel->getEnvironment()));
+        $inputDefinition->addOption(new InputOption('--env', '-e', InputOption::VALUE_REQUIRED, 'The Environment name.', $kernel->getMode()));
+        $inputDefinition->addOption(new InputOption('--mode', null, InputOption::VALUE_REQUIRED, 'The Mode name.', $kernel->getMode()));
         $inputDefinition->addOption(new InputOption('--no-debug', null, InputOption::VALUE_NONE, 'Switches off debug mode.'));
     }
 
@@ -147,7 +148,7 @@ public function all($namespace = null)
      */
     public function getLongVersion()
     {
-        return parent::getLongVersion().sprintf(' (env: <comment>%s</>, debug: <comment>%s</>)', $this->kernel->getEnvironment(), $this->kernel->isDebug() ? 'true' : 'false');
+        return parent::getLongVersion().sprintf(' (mode: <comment>%s</>, debug: <comment>%s</>)', $this->kernel->getMode(), $this->kernel->isDebug() ? 'true' : 'false');
     }
 
     public function add(Command $command)
diff --git a/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php b/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
index 7f3d35d803563..2bb29b07504d7 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php
@@ -69,7 +69,7 @@ trait MicroKernelTrait
     public function getCacheDir(): string
     {
         if (isset($_SERVER['APP_CACHE_DIR'])) {
-            return $_SERVER['APP_CACHE_DIR'].'/'.$this->environment;
+            return $_SERVER['APP_CACHE_DIR'].'/'.$this->mode;
         }
 
         return parent::getCacheDir();
@@ -90,7 +90,7 @@ public function registerBundles(): iterable
     {
         $contents = require $this->getProjectDir().'/config/bundles.php';
         foreach ($contents as $class => $envs) {
-            if ($envs[$this->environment] ?? $envs['all'] ?? false) {
+            if ($envs[$this->mode] ?? $envs['all'] ?? false) {
                 yield new $class();
             }
         }
diff --git a/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php b/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
index 809a85dfdf284..f0acc137a4868 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php
@@ -104,6 +104,10 @@ protected static function createKernel(array $options = [])
 
         if (isset($options['environment'])) {
             $env = $options['environment'];
+        } elseif (isset($_ENV['APP_MODE'])) {
+            $env = $_ENV['APP_MODE'];
+        } elseif (isset($_SERVER['APP_MODE'])) {
+            $env = $_SERVER['APP_MODE'];
         } elseif (isset($_ENV['APP_ENV'])) {
             $env = $_ENV['APP_ENV'];
         } elseif (isset($_SERVER['APP_ENV'])) {
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePoolDeleteCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePoolDeleteCommandTest.php
index 42981c41484f1..6deaf7b706afc 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePoolDeleteCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePoolDeleteCommandTest.php
@@ -18,7 +18,6 @@
 use Symfony\Bundle\FrameworkBundle\Tests\TestCase;
 use Symfony\Component\Console\Tester\CommandTester;
 use Symfony\Component\HttpKernel\CacheClearer\Psr6CacheClearer;
-use Symfony\Component\HttpKernel\KernelInterface;
 
 class CachePoolDeleteCommandTest extends TestCase
 {
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePruneCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePruneCommandTest.php
index 4df5fc024c235..497bea3c07852 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePruneCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/CachePruneCommandTest.php
@@ -18,7 +18,6 @@
 use Symfony\Component\Cache\PruneableInterface;
 use Symfony\Component\Console\Tester\CommandTester;
 use Symfony\Component\DependencyInjection\Argument\RewindableGenerator;
-use Symfony\Component\HttpKernel\KernelInterface;
 
 class CachePruneCommandTest extends TestCase
 {
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/KernelInterface.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/KernelInterface.php
new file mode 100644
index 0000000000000..afdb0a0703155
--- /dev/null
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/KernelInterface.php
@@ -0,0 +1,19 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\FrameworkBundle\Tests\Command;
+
+use Symfony\Component\HttpKernel\KernelInterface as BaseKernelInterface;
+
+interface KernelInterface extends BaseKernelInterface
+{
+    public function getMode(): string;
+}
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/RouterMatchCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/RouterMatchCommandTest.php
index 2505d07881267..6801ef2271e38 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/RouterMatchCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/RouterMatchCommandTest.php
@@ -16,7 +16,6 @@
 use Symfony\Bundle\FrameworkBundle\Command\RouterMatchCommand;
 use Symfony\Bundle\FrameworkBundle\Console\Application;
 use Symfony\Component\Console\Tester\CommandTester;
-use Symfony\Component\HttpKernel\KernelInterface;
 use Symfony\Component\Routing\RequestContext;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationDebugCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationDebugCommandTest.php
index 84e12759ce2fa..c82d5b9fdbd85 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationDebugCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationDebugCommandTest.php
@@ -92,7 +92,7 @@ public function testDebugCustomDirectory()
     {
         $this->fs->mkdir($this->translationDir.'/customDir/translations');
         $this->fs->mkdir($this->translationDir.'/customDir/templates');
-        $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\KernelInterface')->getMock();
+        $kernel = $this->getMockBuilder(KernelInterface::class)->getMock();
         $kernel->expects($this->once())
             ->method('getBundle')
             ->with($this->equalTo($this->translationDir.'/customDir'))
@@ -111,7 +111,7 @@ public function testDebugCustomDirectory()
     public function testDebugInvalidDirectory()
     {
         $this->expectException('InvalidArgumentException');
-        $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\KernelInterface')->getMock();
+        $kernel = $this->getMockBuilder(KernelInterface::class)->getMock();
         $kernel->expects($this->once())
             ->method('getBundle')
             ->with($this->equalTo('dir'))
@@ -170,7 +170,7 @@ function ($path, $catalogue) use ($loadedMessages) {
                 ['foo', $this->getBundle($this->translationDir)],
                 ['test', $this->getBundle('test')],
             ];
-            $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\KernelInterface')->getMock();
+            $kernel = $this->getMockBuilder(KernelInterface::class)->getMock();
             $kernel
                 ->expects($this->any())
                 ->method('getBundle')
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
index 0a86166fc7314..f6dc1366e3573 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/TranslationUpdateCommandTest.php
@@ -17,7 +17,6 @@
 use Symfony\Component\Console\Tester\CommandTester;
 use Symfony\Component\DependencyInjection\Container;
 use Symfony\Component\Filesystem\Filesystem;
-use Symfony\Component\HttpKernel;
 
 class TranslationUpdateCommandTest extends TestCase
 {
@@ -143,7 +142,7 @@ protected function tearDown(): void
     /**
      * @return CommandTester
      */
-    private function createCommandTester($extractedMessages = [], $loadedMessages = [], HttpKernel\KernelInterface $kernel = null, array $transPaths = [], array $viewsPaths = [])
+    private function createCommandTester($extractedMessages = [], $loadedMessages = [], KernelInterface $kernel = null, array $transPaths = [], array $viewsPaths = [])
     {
         $translator = $this->getMockBuilder('Symfony\Component\Translation\Translator')
             ->disableOriginalConstructor()
@@ -189,7 +188,7 @@ function ($path, $catalogue) use ($loadedMessages) {
                 ['foo', $this->getBundle($this->translationDir)],
                 ['test', $this->getBundle('test')],
             ];
-            $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\KernelInterface')->getMock();
+            $kernel = $this->getMockBuilder(KernelInterface::class)->getMock();
             $kernel
                 ->expects($this->any())
                 ->method('getBundle')
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/XliffLintCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/XliffLintCommandTest.php
index 7d6783d9352c0..8223a7ecb217d 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/XliffLintCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/XliffLintCommandTest.php
@@ -19,7 +19,6 @@
 use Symfony\Component\Console\Input\InputDefinition;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Tester\CommandTester;
-use Symfony\Component\HttpKernel\KernelInterface;
 
 /**
  * Tests the part of the XliffLintCommand managed by the FrameworkBundle. The
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/YamlLintCommandTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/YamlLintCommandTest.php
index af81f335e3cdb..e18fbf5de8ee5 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Command/YamlLintCommandTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Command/YamlLintCommandTest.php
@@ -19,7 +19,6 @@
 use Symfony\Component\Console\Input\InputDefinition;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Tester\CommandTester;
-use Symfony\Component\HttpKernel\KernelInterface;
 
 /**
  * Tests the YamlLintCommand.
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Console/ApplicationTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Console/ApplicationTest.php
index ca18462634fb4..0e1eaf135e1b5 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Console/ApplicationTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Console/ApplicationTest.php
@@ -13,6 +13,7 @@
 
 use Symfony\Bundle\FrameworkBundle\Console\Application;
 use Symfony\Bundle\FrameworkBundle\EventListener\SuggestMissingPackageSubscriber;
+use Symfony\Bundle\FrameworkBundle\Tests\Command\KernelInterface;
 use Symfony\Bundle\FrameworkBundle\Tests\TestCase;
 use Symfony\Component\Console\Command\Command;
 use Symfony\Component\Console\Event\ConsoleErrorEvent;
@@ -24,7 +25,6 @@
 use Symfony\Component\Console\Tester\ApplicationTester;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\EventDispatcher\EventDispatcher;
-use Symfony\Component\HttpKernel\KernelInterface;
 
 class ApplicationTest extends TestCase
 {
@@ -264,7 +264,7 @@ private function getKernel(array $bundles, $useDispatcher = false)
             ->willReturnOnConsecutiveCalls([], [])
         ;
 
-        $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\KernelInterface')->getMock();
+        $kernel = $this->getMockBuilder(KernelInterface::class)->getMock();
         $kernel->expects($this->once())->method('boot');
         $kernel
             ->expects($this->any())
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
index 990aa19a13506..191acfff0d908 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
@@ -1627,6 +1627,7 @@ protected function createContainer(array $data = [])
             'kernel.project_dir' => __DIR__,
             'kernel.debug' => false,
             'kernel.environment' => 'test',
+            'kernel.mode' => 'test',
             'kernel.name' => 'kernel',
             'kernel.container_class' => 'testContainer',
             'container.build_hash' => 'Abc1234',
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
index 7dbe15c6c9a5d..916c973f20655 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/app/AppKernel.php
@@ -64,7 +64,7 @@ public function getProjectDir(): string
 
     public function getCacheDir(): string
     {
-        return sys_get_temp_dir().'/'.$this->varDir.'/'.$this->testCase.'/cache/'.$this->environment;
+        return sys_get_temp_dir().'/'.$this->varDir.'/'.$this->testCase.'/cache/'.$this->mode;
     }
 
     public function getLogDir(): string
@@ -84,12 +84,12 @@ protected function build(ContainerBuilder $container)
 
     public function __sleep(): array
     {
-        return ['varDir', 'testCase', 'rootConfig', 'environment', 'debug'];
+        return ['varDir', 'testCase', 'rootConfig', 'mode', 'debug'];
     }
 
     public function __wakeup()
     {
-        $this->__construct($this->varDir, $this->testCase, $this->rootConfig, $this->environment, $this->debug);
+        $this->__construct($this->varDir, $this->testCase, $this->rootConfig, $this->mode, $this->debug);
     }
 
     protected function getKernelParameters(): array
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/app/AppKernel.php b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/app/AppKernel.php
index 72d23f03f30f7..c0008a2026b3e 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/Functional/app/AppKernel.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/Functional/app/AppKernel.php
@@ -22,12 +22,14 @@
  */
 class AppKernel extends Kernel
 {
+    protected $mode;
+
     private $varDir;
     private $testCase;
     private $rootConfig;
     private $authenticatorManagerEnabled;
 
-    public function __construct($varDir, $testCase, $rootConfig, $environment, $debug, $authenticatorManagerEnabled = false)
+    public function __construct($varDir, $testCase, $rootConfig, $mode, $debug, $authenticatorManagerEnabled = false)
     {
         if (!is_dir(__DIR__.'/'.$testCase)) {
             throw new \InvalidArgumentException(sprintf('The test case "%s" does not exist.', $testCase));
@@ -42,7 +44,8 @@ public function __construct($varDir, $testCase, $rootConfig, $environment, $debu
         $this->rootConfig = $rootConfig;
         $this->authenticatorManagerEnabled = $authenticatorManagerEnabled;
 
-        parent::__construct($environment, $debug);
+        $this->mode = $mode;
+        parent::__construct($mode, $debug);
     }
 
     /**
@@ -69,7 +72,7 @@ public function getProjectDir(): string
 
     public function getCacheDir(): string
     {
-        return sys_get_temp_dir().'/'.$this->varDir.'/'.$this->testCase.'/cache/'.$this->environment;
+        return sys_get_temp_dir().'/'.$this->varDir.'/'.$this->testCase.'/cache/'.$this->mode;
     }
 
     public function getLogDir(): string
@@ -92,7 +95,7 @@ public function registerContainerConfiguration(LoaderInterface $loader)
 
     public function serialize()
     {
-        return serialize([$this->varDir, $this->testCase, $this->rootConfig, $this->getEnvironment(), $this->isDebug()]);
+        return serialize([$this->varDir, $this->testCase, $this->rootConfig, $this->mode, $this->isDebug()]);
     }
 
     public function unserialize($str)
diff --git a/src/Symfony/Bundle/TwigBundle/CHANGELOG.md b/src/Symfony/Bundle/TwigBundle/CHANGELOG.md
index be47f246de147..a1c4facb4a23d 100644
--- a/src/Symfony/Bundle/TwigBundle/CHANGELOG.md
+++ b/src/Symfony/Bundle/TwigBundle/CHANGELOG.md
@@ -4,6 +4,8 @@ CHANGELOG
 5.2.0
 -----
 
+ * the `app.env` variable is now runtime-dependent when the `APP_RUNTIME_ENV` env var is defined
+ * added the `app.mode` variable: it's the build-time equivalent of `app.env`
  * deprecated the public `twig` service to private
 
 5.0.0
diff --git a/src/Symfony/Bundle/TwigBundle/Resources/config/twig.php b/src/Symfony/Bundle/TwigBundle/Resources/config/twig.php
index a7124a30c20aa..d8abc696fe7c7 100644
--- a/src/Symfony/Bundle/TwigBundle/Resources/config/twig.php
+++ b/src/Symfony/Bundle/TwigBundle/Resources/config/twig.php
@@ -70,6 +70,7 @@
 
         ->set('twig.app_variable', AppVariable::class)
             ->call('setEnvironment', [param('kernel.environment')])
+            ->call('setMode', [param('kernel.mode')])
             ->call('setDebug', [param('kernel.debug')])
             ->call('setTokenStorage', [service('security.token_storage')->ignoreOnInvalid()])
             ->call('setRequestStack', [service('request_stack')->ignoreOnInvalid()])
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
index 12eaa4ba4c41b..27e6a55691f71 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
@@ -246,6 +246,7 @@ public function testRuntimeLoader()
         $container->registerExtension(new TwigExtension());
         $container->loadFromExtension('twig');
         $container->setParameter('kernel.environment', 'test');
+        $container->setParameter('kernel.mode', 'test');
         $container->setParameter('debug.file_link_format', 'test');
         $container->setParameter('foo', 'FooClass');
         $container->register('http_kernel', 'FooClass');
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/Functional/EmptyAppTest.php b/src/Symfony/Bundle/TwigBundle/Tests/Functional/EmptyAppTest.php
index bfdf9418a765a..55fd8cde8de2f 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/Functional/EmptyAppTest.php
+++ b/src/Symfony/Bundle/TwigBundle/Tests/Functional/EmptyAppTest.php
@@ -69,7 +69,7 @@ public function registerContainerConfiguration(LoaderInterface $loader)
 
     public function getCacheDir(): string
     {
-        return sys_get_temp_dir().'/'.Kernel::VERSION.'/EmptyAppKernel/cache/'.$this->environment;
+        return sys_get_temp_dir().'/'.Kernel::VERSION.'/EmptyAppKernel/cache/'.$this->mode;
     }
 
     public function getLogDir(): string
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/Functional/NoTemplatingEntryTest.php b/src/Symfony/Bundle/TwigBundle/Tests/Functional/NoTemplatingEntryTest.php
index b571d1cc76094..df0e9813c7d6b 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/Functional/NoTemplatingEntryTest.php
+++ b/src/Symfony/Bundle/TwigBundle/Tests/Functional/NoTemplatingEntryTest.php
@@ -77,7 +77,7 @@ public function registerContainerConfiguration(LoaderInterface $loader)
 
     public function getCacheDir(): string
     {
-        return sys_get_temp_dir().'/'.Kernel::VERSION.'/NoTemplatingEntryKernel/cache/'.$this->environment;
+        return sys_get_temp_dir().'/'.Kernel::VERSION.'/NoTemplatingEntryKernel/cache/'.$this->mode;
     }
 
     public function getLogDir(): string
diff --git a/src/Symfony/Bundle/TwigBundle/composer.json b/src/Symfony/Bundle/TwigBundle/composer.json
index 0297efaeb8f47..1aecce77cbe73 100644
--- a/src/Symfony/Bundle/TwigBundle/composer.json
+++ b/src/Symfony/Bundle/TwigBundle/composer.json
@@ -20,7 +20,7 @@
         "symfony/config": "^4.4|^5.0",
         "symfony/twig-bridge": "^5.0",
         "symfony/http-foundation": "^4.4|^5.0",
-        "symfony/http-kernel": "^5.0",
+        "symfony/http-kernel": "^5.2",
         "symfony/polyfill-ctype": "~1.8",
         "twig/twig": "^2.10|^3.0"
     },
diff --git a/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/config.html.twig b/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/config.html.twig
index 4e4a59d1b3ce4..56746f3678fae 100644
--- a/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/config.html.twig
+++ b/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/config.html.twig
@@ -38,7 +38,14 @@
                 </span>
             </div>
 
-            {% if 'n/a' is not same as(collector.env) %}
+            {% if collector.mode is defined %}
+                {% if 'n/a' is not same as(collector.mode) %}
+                    <div class="sf-toolbar-info-piece">
+                        <b>Mode</b>
+                        <span>{{ collector.mode }}</span>
+                    </div>
+                {% endif %}
+            {% elseif 'n/a' is not same as(collector.env) %}
                 <div class="sf-toolbar-info-piece">
                     <b>Environment</b>
                     <span>{{ collector.env }}</span>
@@ -116,7 +123,14 @@
             <span class="label">Symfony version</span>
         </div>
 
-        {% if 'n/a' != collector.env %}
+        {% if collector.mode is defined %}
+            {% if 'n/a' is not same as(collector.mode) %}
+                <div class="metric">
+                    <span class="value">{{ collector.mode }}</span>
+                    <span class="label">Mode</span>
+                </div>
+            {% endif %}
+        {% elseif 'n/a' != collector.env %}
             <div class="metric">
                 <span class="value">{{ collector.env }}</span>
                 <span class="label">Environment</span>
diff --git a/src/Symfony/Component/HttpKernel/CHANGELOG.md b/src/Symfony/Component/HttpKernel/CHANGELOG.md
index a655e2d6f945a..30776b6745577 100644
--- a/src/Symfony/Component/HttpKernel/CHANGELOG.md
+++ b/src/Symfony/Component/HttpKernel/CHANGELOG.md
@@ -1,6 +1,16 @@
 CHANGELOG
 =========
 
+5.3.0
+-----
+
+ * made parameter `kernel.environment` runtime-dependent when the `APP_RUNTIME_ENV` env var is set
+ * added parameter `kernel.mode`: it's the build-time equivalent of `kernel.environment`
+ * deprecated the `Kernel::$environment` property, use `Kernel::$mode` instead
+ * deprecated the `KernelInterface::getEnvironment()` method, use `KernelInterface::getMode()` instead
+ * deprecated the `ConfigDataCollector::getEnv()` method, use `ConfigDataCollector::getMode()` instead
+
+
 5.2.0
 -----
 
diff --git a/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php b/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
index ba0a3eec6e0c8..a136d4f2e7546 100644
--- a/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
+++ b/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
@@ -46,7 +46,7 @@ public function collect(Request $request, Response $response, \Throwable $except
             'token' => $response->headers->get('X-Debug-Token'),
             'symfony_version' => Kernel::VERSION,
             'symfony_state' => 'unknown',
-            'env' => isset($this->kernel) ? $this->kernel->getEnvironment() : 'n/a',
+            'mode' => isset($this->kernel) ? $this->kernel->getMode() : 'n/a',
             'debug' => isset($this->kernel) ? $this->kernel->isDebug() : 'n/a',
             'php_version' => \PHP_VERSION,
             'php_architecture' => \PHP_INT_SIZE * 8,
@@ -207,14 +207,23 @@ public function getPhpTimezone()
         return $this->data['php_timezone'];
     }
 
+    public function getMode(): string
+    {
+        return $this->data['mode'];
+    }
+
     /**
      * Gets the environment.
      *
      * @return string The environment
+     *
+     * @deprecated since Symfony 5.2, use getMode() instead.
      */
     public function getEnv()
     {
-        return $this->data['env'];
+        trigger_deprecation('symfony/http-kernel', '5.2', 'The "%s()" method is deprecated, use getMode() instead.', __METHOD__);
+
+        return $this->data['mode'];
     }
 
     /**
diff --git a/src/Symfony/Component/HttpKernel/Kernel.php b/src/Symfony/Component/HttpKernel/Kernel.php
index ad9a4b2d78a5b..c2c404f03b8d6 100644
--- a/src/Symfony/Component/HttpKernel/Kernel.php
+++ b/src/Symfony/Component/HttpKernel/Kernel.php
@@ -47,9 +47,9 @@ class_exists(ConfigCache::class);
 /**
  * The Kernel is the heart of the Symfony system.
  *
- * It manages an environment made of bundles.
+ * It manages a mode made of bundles.
  *
- * Environment names must always start with a letter and
+ * Mode names must always start with a letter and
  * they must only contain letters and numbers.
  *
  * @author Fabien Potencier <fabien@symfony.com>
@@ -62,10 +62,15 @@ abstract class Kernel implements KernelInterface, RebootableInterface, Terminabl
     protected $bundles = [];
 
     protected $container;
-    protected $environment;
     protected $debug;
     protected $booted = false;
     protected $startTime;
+    protected $mode;
+
+    /**
+     * @deprecated since Symfony 5.2, use $mode instead
+     */
+    protected $environment;
 
     private $projectDir;
     private $warmupDir;
@@ -84,9 +89,10 @@ abstract class Kernel implements KernelInterface, RebootableInterface, Terminabl
     const END_OF_MAINTENANCE = '07/2021';
     const END_OF_LIFE = '07/2021';
 
-    public function __construct(string $environment, bool $debug)
+    public function __construct(string $mode, bool $debug)
     {
-        $this->environment = $environment;
+        $this->mode = $mode;
+        $this->environment = $mode;
         $this->debug = $debug;
     }
 
@@ -257,10 +263,22 @@ public function locateResource(string $name)
 
     /**
      * {@inheritdoc}
+     *
+     * @deprecated since Symfony 5.2, use getMode() instead.
      */
     public function getEnvironment()
     {
-        return $this->environment;
+        trigger_deprecation('symfony/http-kernel', '5.2', 'The "%s()" method is deprecated, use getMode() instead.', __METHOD__);
+
+        return $this->mode;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getMode(): string
+    {
+        return $this->mode;
     }
 
     /**
@@ -331,7 +349,7 @@ public function getStartTime()
      */
     public function getCacheDir()
     {
-        return $this->getProjectDir().'/var/cache/'.$this->environment;
+        return $this->getProjectDir().'/var/cache/'.$this->mode;
     }
 
     /**
@@ -405,10 +423,10 @@ protected function getContainerClass()
     {
         $class = static::class;
         $class = false !== strpos($class, "@anonymous\0") ? get_parent_class($class).str_replace('.', '_', ContainerBuilder::hash($class)) : $class;
-        $class = str_replace('\\', '_', $class).ucfirst($this->environment).($this->debug ? 'Debug' : '').'Container';
+        $class = str_replace('\\', '_', $class).ucfirst($this->mode).($this->debug ? 'Debug' : '').'Container';
 
         if (!preg_match('/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/', $class)) {
-            throw new \InvalidArgumentException(sprintf('The environment "%s" contains invalid characters, it can only contain characters allowed in PHP class names.', $this->environment));
+            throw new \InvalidArgumentException(sprintf('The mode "%s" contains invalid characters, it can only contain characters allowed in PHP class names.', $this->mode));
         }
 
         return $class;
@@ -605,7 +623,8 @@ protected function getKernelParameters()
 
         return [
             'kernel.project_dir' => realpath($this->getProjectDir()) ?: $this->getProjectDir(),
-            'kernel.environment' => $this->environment,
+            'kernel.environment' => 'env(default:kernel.mode:APP_RUNTIME_ENV)',
+            'kernel.mode' => $this->mode,
             'kernel.debug' => $this->debug,
             'kernel.build_dir' => realpath($buildDir = $this->warmupDir ?: $this->getBuildDir()) ?: $buildDir,
             'kernel.cache_dir' => realpath($this->getCacheDir()) ?: $this->getCacheDir(),
@@ -854,11 +873,11 @@ public static function stripComments(string $source)
      */
     public function __sleep()
     {
-        return ['environment', 'debug'];
+        return ['mode', 'debug'];
     }
 
     public function __wakeup()
     {
-        $this->__construct($this->environment, $this->debug);
+        $this->__construct($this->environment ?? $this->mode, $this->debug);
     }
 }
diff --git a/src/Symfony/Component/HttpKernel/KernelInterface.php b/src/Symfony/Component/HttpKernel/KernelInterface.php
index c1be3aff43ee0..a0932d1c3a5f3 100644
--- a/src/Symfony/Component/HttpKernel/KernelInterface.php
+++ b/src/Symfony/Component/HttpKernel/KernelInterface.php
@@ -23,6 +23,7 @@
  * @method string getBuildDir() Returns the build directory - not implementing it is deprecated since Symfony 5.2.
  *                              This directory should be used to store build artifacts, and can be read-only at runtime.
  *                              Caches written at runtime should be stored in the "cache directory" ({@see KernelInterface::getCacheDir()}).
+ * @method string getMode()
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
@@ -91,6 +92,8 @@ public function locateResource(string $name);
      * Gets the environment.
      *
      * @return string The current environment
+     *
+     * @deprecated since Symfony 5.2, use getMode() instead.
      */
     public function getEnvironment();
 
diff --git a/src/Symfony/Component/HttpKernel/Tests/DataCollector/ConfigDataCollectorTest.php b/src/Symfony/Component/HttpKernel/Tests/DataCollector/ConfigDataCollectorTest.php
index 308a20127acf2..d6c1f23cbaa7e 100644
--- a/src/Symfony/Component/HttpKernel/Tests/DataCollector/ConfigDataCollectorTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/DataCollector/ConfigDataCollectorTest.php
@@ -27,7 +27,7 @@ public function testCollect()
         $c->setKernel($kernel);
         $c->collect(new Request(), new Response());
 
-        $this->assertSame('test', $c->getEnv());
+        $this->assertSame('test', $c->getMode());
         $this->assertTrue($c->isDebug());
         $this->assertSame('config', $c->getName());
         $this->assertMatchesRegularExpression('~^'.preg_quote($c->getPhpVersion(), '~').'~', \PHP_VERSION);
diff --git a/src/Symfony/Component/HttpKernel/Tests/KernelTest.php b/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
index beb4b9fe3fa66..f5bcc7f6c7707 100644
--- a/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
@@ -40,11 +40,11 @@ protected function tearDown(): void
 
     public function testConstructor()
     {
-        $env = 'test_env';
+        $mode = 'test_mode';
         $debug = true;
-        $kernel = new KernelForTest($env, $debug);
+        $kernel = new KernelForTest($mode, $debug);
 
-        $this->assertEquals($env, $kernel->getEnvironment());
+        $this->assertEquals($mode, $kernel->getMode());
         $this->assertEquals($debug, $kernel->isDebug());
         $this->assertFalse($kernel->isBooted());
         $this->assertLessThanOrEqual(microtime(true), $kernel->getStartTime());
@@ -52,13 +52,13 @@ public function testConstructor()
 
     public function testClone()
     {
-        $env = 'test_env';
+        $mode = 'test_mode';
         $debug = true;
-        $kernel = new KernelForTest($env, $debug);
+        $kernel = new KernelForTest($mode, $debug);
 
         $clone = clone $kernel;
 
-        $this->assertEquals($env, $clone->getEnvironment());
+        $this->assertEquals($mode, $clone->getMode());
         $this->assertEquals($debug, $clone->isDebug());
         $this->assertFalse($clone->isBooted());
         $this->assertLessThanOrEqual(microtime(true), $clone->getStartTime());
@@ -67,11 +67,11 @@ public function testClone()
     public function testClassNameValidityGetter()
     {
         $this->expectException('InvalidArgumentException');
-        $this->expectExceptionMessage('The environment "test.env" contains invalid characters, it can only contain characters allowed in PHP class names.');
-        // We check the classname that will be generated by using a $env that
+        $this->expectExceptionMessage('The mode "test.mode" contains invalid characters, it can only contain characters allowed in PHP class names.');
+        // We check the classname that will be generated by using a $mode that
         // contains invalid characters.
-        $env = 'test.env';
-        $kernel = new KernelForTest($env, false, false);
+        $mode = 'test.mode';
+        $kernel = new KernelForTest($mode, false, false);
 
         $kernel->boot();
     }
@@ -310,10 +310,10 @@ public function doStuff()
 
     public function testSerialize()
     {
-        $env = 'test_env';
+        $mode = 'test_mode';
         $debug = true;
-        $kernel = new KernelForTest($env, $debug);
-        $expected = "O:57:\"Symfony\Component\HttpKernel\Tests\Fixtures\KernelForTest\":2:{s:14:\"\0*\0environment\";s:8:\"test_env\";s:8:\"\0*\0debug\";b:1;}";
+        $kernel = new KernelForTest($mode, $debug);
+        $expected = "O:57:\"Symfony\Component\HttpKernel\Tests\Fixtures\KernelForTest\":2:{s:7:\"\0*\0mode\";s:9:\"test_mode\";s:8:\"\0*\0debug\";b:1;}";
         $this->assertEquals($expected, serialize($kernel));
     }
 
@@ -671,9 +671,9 @@ class CustomProjectDirKernel extends Kernel implements WarmableInterface
     private $buildContainer;
     private $httpKernel;
 
-    public function __construct(\Closure $buildContainer = null, HttpKernelInterface $httpKernel = null, $env = 'custom')
+    public function __construct(\Closure $buildContainer = null, HttpKernelInterface $httpKernel = null, $mode = 'custom')
     {
-        parent::__construct($env, true);
+        parent::__construct($mode, true);
 
         $this->buildContainer = $buildContainer;
         $this->httpKernel = $httpKernel;