PHP superglobal variables are built-in variables that are always available in all scopes throughout a script. They provide an easy way to access data from anywhere in the script.
Examples of superglobal variables are:
$_GET – An array of variables passed to the current script via the URL parameters
$_POST – An array of variables passed to the current script via the HTTP POST method
$_COOKIE – An array of variables passed to the current script via HTTP Cookies
$_SESSION – An array of session variables available to the current script
$_ENV – An array of variables passed to the current script via the environment method