Superglobal variables in PHP are built-in predefined variables that may be accessed throught a script's scope.

List of PHP Superglobals
SUPERGLOBAL DESCRIPTION
$_COOKIE Approaches cookie data.
$_ENV Approaches a parser's environment.
$_FILES Approaches files being uploaded to a server.
$_GET Returns the name of $_GET variable.
$_POST Returns the name of $_POST variable.
$_REQUEST Requests a value of a variable.
$_SERVER Contains information about a server.
$_SESSION Approaches session data.
$GLOBALS Approaches all global variables.