Taking a dump on the closed lid of a toilet. Usually performed in someone else's dorm or barracks.
You go into a toilet stall, close the door, put the seat and the lid down, and poop on the lid. This is called top shelfing it. Then you go to another stall and take care of the clean up work. Wash your hands, and sneak out of the bathroom unnoticed. Works best in the middle of the night.