$_REQUEST and $_POST ???

The difference is $_REQUEST and $_POST is that $_REQUEST gets $_POST, $_GET, and $_COOKIE.

This sometimes can be useful, but it can also be dangerous, because if you weren't expecting to get a GET or COOKIE param, and you use REQUEST, you're getting it.

For security reasons, it's best to limit form inputs to exactly what you expect, and only what you expect to pass through the form.

So general practice you'll find people use POST, GET, and COOKIE when that's what they expect. I would limit using REQUEST to when you have a reason to use it, like lets say your form has a GET param that ref url in it, but the rest of the form posts via POST, than REQUEST makes sense so you can receive all the params. Just be prepared to handle any extra params that might come in, maliciously.

Which by the way, even if you use POST, GET, or COOKIE, someone still can send in malicious parmas, so you always have to sanitize, every single time.