Godwin's law (also Godwin's rule of Nazi analogies) is an adage in Internet culture that was originated by Mike Godwin in 1990. The law states that:
As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1 (i.e. certainty).
There is a tradition in many Usenet newsgroups that once such a comparison is made, the thread is over, and whoever mentioned the Nazis has automatically lost whatever argument was in progress.