Session

Session support in PHP consists of a way to preserve certain data across subsequent accesses.

It relies on the session_* functions, and the $_SESSION superglobal variable.

<?php

if (isset($_SESSION['x'])) {
    print "x was already set with the value ".$_SESSION['x'];
}

$_SESSION['x'] = rand(0, 10);
print "Giving the value ".$_SESSION['x']." to x, in the session\n";

?>

Documentation

See also Session in PHP: Creating, Destroying, and Working With Session in PHP

Related : Superglobal Variables