Alt-F4

While you are in the Alt-space menu, you'’ll notice that almost every Windows application has a "“Close"” menu item (note their underlining of the letter C), but note too that there is a direct shortcut key -– the Alt key with the F4 function key.

Alt-F4 will close just about any Windows Application. If you have data or documents that ought to be saved, you'’ll be prompted.

Alt-F4 is a fast way of shutting down an application you no longer need, although my preference is to leave them all open and use Alt-Tab to go to the one I want.

"Never Close, Never Minimize" is my motto.
Let Windows do the memory-management thing.