TRIVIAL PURSUITS: What does the ‘D’ in ‘D-Day’ stand for?

What does the ‘D’ stand for in ‘D-Day?’

It doesn’t stand for anything.  If you go to http://www.dtic.mil/doctrine/dod_dictionary and search for D-Day, you’ll find that the Department of Defense defines it as “The unnamed day on which a particular operation commences or is to commence.”