I am currently using add_submenu_page to add pages for my plugin. However, I wish to create a page that don’t appear in the admin menu, is that possible?

1
Set the parent_slug
property to null
, example;
add_submenu_page(
null // -> Set to null - will hide menu link
, 'Page Title' // -> Page Title
, 'Menu Title' // -> Title that would otherwise appear in the menu
, 'administrator' // -> Capability level
, 'menu_handle' // -> Still accessible via admin.php?page=menu_handle
, 'page_callback' // -> To render the page
);
This will hide the sub menu page from your parent (top level) menu link.
It does not state this in the Codex entry for add_submenu_page
though.
It now states this in the Codex entry for add_submenu_page
(thanks goto Ian Dunn).