These constants are defined by the PHP core. This includes PHP, the Zend engine, and SAPI modules.
PHP_VERSION 
      (string)
     PHP_MAJOR_VERSION 
      (integer)
     PHP_MINOR_VERSION 
      (integer)
     PHP_RELEASE_VERSION 
      (integer)
     PHP_VERSION_ID 
      (integer)
     PHP_EXTRA_VERSION 
      (string)
     PHP_ZTS 
      (integer)
     PHP_DEBUG 
      (integer)
     PHP_MAXPATHLEN 
      (integer)
     PHP_OS 
      (string)
     PHP_SAPI 
      (string)
     PHP_EOL 
      (string)
     PHP_INT_MAX 
      (integer)
     PHP_INT_MIN 
      (integer)
     PHP_INT_SIZE 
      (integer)
     DEFAULT_INCLUDE_PATH 
      (string)
     PEAR_INSTALL_DIR 
      (string)
     PEAR_EXTENSION_DIR 
      (string)
     PHP_EXTENSION_DIR 
      (string)
     PHP_PREFIX 
      (string)
     PHP_BINDIR 
      (string)
     PHP_BINARY 
      (string)
     PHP_MANDIR 
      (string)
     PHP_LIBDIR 
      (string)
     PHP_DATADIR 
      (string)
     PHP_SYSCONFDIR 
      (string)
     PHP_LOCALSTATEDIR 
      (string)
     PHP_CONFIG_FILE_PATH 
      (string)
     PHP_CONFIG_FILE_SCAN_DIR 
      (string)
     PHP_SHLIB_SUFFIX 
      (string)
     E_ERROR 
      (integer)
     E_WARNING 
      (integer)
     E_PARSE 
      (integer)
     E_NOTICE 
      (integer)
     E_CORE_ERROR 
      (integer)
     E_CORE_WARNING 
      (integer)
     E_COMPILE_ERROR 
      (integer)
     E_COMPILE_WARNING 
      (integer)
     E_USER_ERROR 
      (integer)
     E_USER_WARNING 
      (integer)
     E_USER_NOTICE 
      (integer)
     E_DEPRECATED 
      (integer)
     E_USER_DEPRECATED 
      (integer)
     E_ALL 
      (integer)
     E_STRICT
      (integer)
     __COMPILER_HALT_OFFSET__
      (integer)
     TRUE
      (boolean)
     FALSE
      (boolean)
     NULL
      (null)
     See also: Magic constants.
All constants from core extensions are defined in PHP by default.