Menus are custom toolbars that you can create and assign to multiple documents. They are comprised of menu items, which can be assigned different tasks to perform.
Menus can be used for:
Linking related documents together to create a microsite
Providing sectional navigation for a single document
Linking out to other websites that support the document(s), for example - your intranet.
A menu is set at document level and will be applied to every version in a document. Different menus cannot be applied to individual versions.