superglobal

A superglobal is a term used in PHP to describe a set of built-in variables that are automatically available in all scopes of a script. They are global and accessible from any function, class method, included file, or code block without requiring a global declaration. Superglobals are populated by PHP from request data, user input, or environment information and are typically arrays or array-like structures.

PHP defines several superglobals, the most commonly used being $_GET, $_POST, $_COOKIE, $_REQUEST, $_SESSION, $_FILES, $_SERVER, $_ENV, and $GLOBALS. $_GET and $_POST contain data submitted by the client in the query string or form submissions. $_COOKIE stores cookies sent by the client. $_SESSION stores session data. $_FILES contains information about uploaded files. $_SERVER provides request and server information such as method and script path. $_ENV contains environment variables. $_REQUEST is a merged view of $_GET, $_POST, and $_COOKIE, depending on configuration. $GLOBALS references all global variables.

Access to these variables is simple, for example reading a query parameter with $_GET['id'] or a submitted form field with $_POST['name']. However, because their contents come from clients or the server environment, they should be validated, sanitized, or escaped as appropriate before use in output, database queries, or file operations.

Superglobals are a core feature of PHP and are distinct from ordinary variables by being always accessible across scopes. The concept is primarily associated with PHP, though other languages have global or context-specific variables with analogous behavior.