Originally posted by Remote_Access_
Hehe, it's a trick question. UNIX is not an acronym therefore does not short for anything. An early versions of UNIX was actually called UNICS and it was short for UNiplexed Information and Computing Service. Additional information about UNIX can be found on this page.
Some more information about UNICS a.k.a. UNIX :-).

Unix is a "play on words" of an older multi user time-sharing OS known as Multics. UNIX was also originally designed as a single user environment (hence "U"nix).

Nice post Remote_Access_ , the history has a lot to tell us about the future !!