A novice question

so you did try searching for: $_GET['form'], $form, $HTTP_GET_VARS['form'], $_REQUEST['form'] ?
hmmz.. okej, all that is useless: search for: form (no quots, no $ )
well yes, everything in url after? is a $_GET variables and their values, however not ALWAYS you will be able to see values, sometimes you just set the variable's name.

it is also possible that form variable is used in some included files... as they will also be able to take a use of superglobals.