Register Globals
Register globals is an old and removed feature of PHP, which automatically created variables from the incoming super globals, such as $_GET, $_POST, $_REQUEST, $_COOKIES.
This meant that the initial set of variables in an application was not known, as they would depend on the incoming data.
Register globals has been removed in version 5.4.
<?php
// $_GET['foo'] = 'bar';
echo $foo;
// $_GET['_SESSION']['logged'] = '1';
?>