ROT13

A way of encoding bad jokes, movie reviews that give away the ending, pornography, or anything else that may offend some users. It is a cryptography system that scrambles your text so that a casual, over-the-shoulder reader cannot read it.

Essentially, each letter of a message is replaced by the thirteenth letter away from it in the alphabet. There are online decoders to read these; most Usenet news readers and other posting programs, as well as some browsers and e-mail programs, include a rot-13 feature. A major advantage of rot-13 is that the same code can be used for encoding and decoding.