rot13 /rot ther'teen/ n.,v.
[Usenet: from `rotate alphabet 13 places'] The simple
Caesar-cypher encryption that replaces each English letter with
the one 13 places forward or back along the alphabet, so that
"The butler did it!" becomes "Gur ohgyre qvq vg!" Most Usenet
news reading and posting programs include a rot13 feature. It is
used to enclose the text in a sealed wrapper that the reader must
choose to open -- e.g., for posting things that might offend some
readers, or spoilers. A major
advantage of rot13 over rot(N) for other N is that it is
self-inverse, so the same code can be used for encoding and
decoding. See also spoiler
space, which has partly displaced rot13 since
non-Unix-based newsreaders became common.