A term that originated on Usenet, Godwin's Law states that as an online argument grows longer and more heated, it becomes increasingly likely that somebody will bring up Adolf Hitler or the Nazis. When such an event occurs, the person guilty of invoking Godwin's Law has effectively forfieted the argument.

Usenet There is a tradition in many groups that, once this occurs, that thread is over, and whoever mentioned the Nazis has automatically lost whatever argument was in progress. Godwin's Law thus practically guarantees the existence of an upper bound on thread length in those groups. However there is also a widely- recognized codicil that any intentional triggering of Godwin's Law in order to invoke its thread-ending effects will be unsuccessful.