PHP Superglobals
Global variables available everywhere.
PHP Global Variables - Superglobals
Some predefined variables in PHP are "superglobals", which means that they are always accessible, regardless of scope - and you can access them from any function, class or file without having to do anything special.
The PHP superglobal variables are:
$GLOBALS$_SERVER$_REQUEST$_POST$_GET$_FILES$_ENV$_COOKIE$_SESSION
$_SERVER
$_SERVER is a PHP super global variable which holds information about headers, paths, and script locations.
$_REQUEST
$_REQUEST is a PHP super global variable which is used to collect data after submitting an HTML form.