(PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)
$_REQUEST — HTTP Request variables
This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods.
The variables in $_REQUEST are provided to the script via the GET, POST, and COOKIE input mechanisms and therefore could be modified by the remote user and cannot be trusted. The presence and order of variables listed in this array is defined according to the PHP request_order, and variables_order configuration directives.