A cascading menu (also referred to as a hierarchical menu or child menu) is a submenu of a menu item. The visual cue for a cascading menu is the inclusion of a triangular arrow display adjacent to the label of its parent menu item.
You can use cascading menus to provide user access to additional choices rather than taking up additional space in the parent menu. They may also be useful for displaying hierarchically related objects.
Be aware that cascading menus can add complexity to the menu interface by requiring the user to navigate further through the menu structure to get to a particular choice. Cascading menus also require more coordination to handle the changes in direction necessary to navigate through them.
In light of these design tradeoffs, use cascading menus sparingly. Minimize the number of levels for any given menu item, ideally limiting your design to a single submenu. Avoid using cascading menus for frequent, repetitive commands.
As an alternative, make choices available in a secondary window, particularly when the choices are independent settings; this allows the user to set multiple options in one invocation of a command. You can also support many common options as entries on a toolbar.
The user interaction for a cascading menu is similar to that of a drop-down menu from the menu bar, except a cascading menu displays after a short time-out. This avoids the unnecessary display of the menu if the user is browsing or navigating to another item in the parent menu. Once displayed, if the user moves the pointer to another menu item, the cascading menu is removed after a short time-out. This time-out enables the user to directly drag from the parent menu into an entry in its cascading menu.