PHPMaster.com: Introducing Superglobals
PHPMaster.com is back with another introductory tutorial for those new to the PHP language. It's a look at one of the most commonly used (sometimes badly) features of the language - superglobal variables.
Superglobals are specially-defined array variables in PHP that make it easy for you to get information about a request or its context. They are called superglobal because they are always accessible, regardless of the scope - that is, you can access them from any function, class or file without having to do anything special. The superglobal variables are: $GLOBALS, $_SERVER, $_GET, $_POST, $_FILES, $_COOKIE, $_SESSION, $_REQUEST and $_ENV. And while you can learn more about each by reading the PHP documentation, I'd like to show you the ones I think you're likely use the most.
He goes through some of the major ones and explains what kind of situations they can be used in and what data would be inside - $_POST, $_GET, $_SESSION and $_SERVER.