P.W.N.E.D. is often written after the statement of a definition or description. Each letter stands for:
(this P.W.N.E.D. once again stands for P.W.N.E.D. With Necessary Erat Demonstrandum, and so on Ad infinitum)
See modus pwnens for example. Also the definition above is an example for the use of P.W.N.E.D.