Menus:
The menu module is a collection of objects like as menu items, sub menu items, sub menus, and PL/SQL code blocks.
PL/SQL Libraries
The library module is a set of PL/SQL procedures and functions stored in a single library file. This library file is then attached to a form or menu module. All other objects in the form or menu can now access and share the collection of PL/SQL procedures and functions.