ROT13 ("rotate by 13 places", sometimes hyphenated ROT-13)'s a simple substitution cipher used in online forums as a means of hiding spoilers, punchlines, puzzle solutions, and offensive materials from the casual glance. ROT13 has been described as the "Usenet equivalent of a magazine printing the answer to a quiz upside down". ROT13's a variation of the Caesar cipher, developed in ancient Rome. ROT13's its own inverse; that's, to undo ROT13, the same algorithm's applied, so the same action can… (More on Rot13)