MENU_CUSTOM_MENU
in includes/menu.inc
Custom menus are those defined by the administrator. Reserved for internal use; do not return from hook_menu() implementations.
<?php
define('MENU_CUSTOM_MENU', MENU_IS_ROOT | MENU_VISIBLE_IN_TREE | MENU_CREATED_BY_ADMIN | MENU_MODIFIABLE_BY_ADMIN);
?>