Menus are lists of menu items that can be created within your interface, you can create as many menus as you need, and once created can render them throughout your interface using blocks or render them manually in code through use the <ux-menu-list/> and <ux-link/> components provided in the UI Kit.
You can find documentation for the Menu List element here
Each Menu has a unique key that allows you to access it programmatically from the $sdk.app.menus service. Having a key ensures that even if you change the title or configuration of a menu it won't break any reference links where it has been rendered within the interface.
Each Menu can have an unlimited number of child menu items. These menu items can link to either an internal route within your interface or an external absolute url.
Menus are created and managed in the interface builder through use of the Menu Sidebar.