what exactly is $_REQUEST[$K] in PHP?

[gr8scottishguy]

\[code\]$_REQUEST[$k] = isset($_GET[$k]) ? $_GET[$k] : $_POST[$k];\[/code\]or \[code\]$_REQUEST[$k] = isset($_POST[$k]) ? $_POST[$k] : $_GET[$k];\[/code\]Which is the case,reason?