It is a menu that is part of another menu. So you can have main menu and when you choose one of its items and it shows another menu, that is a sub-menu. It is more a part of versions of Excel up to version 2003. So, for example, on the Edit menu there was a sub-menu with options for Fill.
A submenu command
but what is the answer
A submenu is a secondary menu that appears while you are holding the cursor over an item on the primary menu.
Submenu
potato
Submenu
its shows architecture of the program
submenu
Submenu
Programs that can be opened
A right arrow.
submenu