Pronounced "Moo-sih-fur"... A slang term for the most ridiculously disturbing thing that should be silly, but is actually quite... scary.
The origins of this concept name come from a MUD called World's End where you could actually choose a cow as a player race. The only thing you could really do as a cow was graze, move about, and moo at people. Needless to say, it wasn't a real popular choice. However, one enterprising player decided to choose it, and describe himself as, basically a very evil looking cow with fire in place of its eyes, blood-red horns and hooves, and a keening moo that brought terror to the very depths of one's soul...
...in point of fact, it was the most disturbing character on the entire MUD and quickly replaced Shai'tan as the most feared presence on the server.