This is a word that is ment to describe a large number a zombies that crowd around you or an opening. It is a combination of "zombie" and "orgy" because lets face it, it does look like they are having an orgy. Most commonly seen in Call Of Duty: World at War on any of the Nazi Zombies levels.
Alex: "Shit. I just died. Heads up, zombies comming your way."
Damian: "Alex you douche! I have a whole zorgy following me!"
Joe: "fail. lawl"