$_SESSION -- $HTTP_SESSION_VARS [deprecated] — Session variables
An associative array containing session variables available to
the current script. See the Session
functions documentation for more information on how this
$HTTP_SESSION_VARS contains the same initial
information, but is not a superglobal.
(Note that $HTTP_SESSION_VARS and $_SESSION
are different variables and that PHP handles them as such)
Introduced $_SESSION that the deprecated
Note: This is a 'superglobal', or
automatic global, variable. This simply means that it is available in
all scopes throughout a script. There is no need to do
global $variable; to access it within functions or methods.