Godwin's law (also known as Godwin's Rule of Nazi Analogies or Godwin's law of Nazi Analogies) is an observation made by Mike Godwin in 1990 which has become an Internet adage. It states: "As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches.
For example, there is a tradition in many newsgroups and other Internet discussion forums that once such a comparison is made, the thread is finished and whoever mentioned the Nazis has automatically "lost" whatever debate was in progress.