php super global variables

Many predefined variables in PHP are "superglobal", which means they are available throughout the entire scope of a script. They can be accessed within a function or method without executing global $variable;.
These super global variables are:
$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION

$GLOBALS This kind of global variable is used in any PHP script Positional access to global variables (either from a function or method).
PHP stores all global variables in an array named $GLOBALS[index]. The name of the variable is the key of the array.

<?php 
$x = 75; 
$y = 25;
 
function addition() { 
  $GLOBALS[&#39;z&#39;] = $GLOBALS[&#39;x&#39;] + $GLOBALS[&#39;y&#39;]; 
}
 
addition(); 
echo $z; 
?>