Shortened form of Non Sortie Producing Motherfucker. Term created by the "working" side of the U.S. Air Force. A sortie is one take-off and landing of an aircraft. Those that don't work on the flightline do not produce sorties and are thus labelled nonners.
Dad, what did you do during the war?
Son, I counted batteries in a box on a shelf. If there aren't 12 batteries in that box, it's my job to tell someone about it.