Superglobals — Superglobals are built-in variables that are always available in all scopes
Several predefined variables in PHP are "superglobals", which means they
are available in all scopes throughout a script. There is no need to do
global $variable; to access them within functions
These superglobal variables are:
Superglobals were introduced to PHP.
By default, all of the superglobals are available but there are
directives that affect this availability. For further information, refer
to the documentation for
Dealing with register_globals
If the deprecated register_globals
directive is set to on then the variables within will
also be made available in the global scope of the script. For example,
$_POST['foo'] would also exist as $foo.
For related information, see the FAQ titled
"How does register_globals affect me?"
Superglobals cannot be used as
inside functions or class methods.