The "World" menu is shown when the user clicks the Red button anywhere on the desktop (outside of a window) in Morphic.
The World menu contains a number of useful submenus, and is the starting point for a lot of globally-accessible functionality in Squeak.
World menu in version 3.8
In terms of implementation, an instance of the class TheWorldMenu is shown when clicking on the desktop (actually the World, an instance of PasteUpMorph).
(A similar menu also appears in MVC when clicking on the desktop, although it's a bit smaller than the World menu in Morphic.)