The Jargon File (version 4.4.7, 29 Dec 2003):

quux
 /kwuhks/, n.

    [Mythically, from the Latin semi-deponent verb quuxo, quuxare, quuxandum
    iri; noun form variously ?quux? (plural ?quuces?, anglicized to ?quuxes?)
    and ?quuxu? (genitive plural is ?quuxuum?, for four u-letters out of seven
    in all, using up all the ?u? letters in Scrabble).]

    1. Originally, a metasyntactic variable like foo and foobar. Invented
    by Guy Steele for precisely this purpose when he was young and naive and
    not yet interacting with the real computing community. Many people invent
    such words; this one seems simply to have been lucky enough to have spread
    a little. In an eloquent display of poetic justice, it has returned to the
    originator in the form of a nickname.

    2. interj. See foo; however, denotes very little disgust, and is uttered
    mostly for the sake of the sound of it.

    3. Guy Steele in his persona as ?The Great Quux?, which is somewhat
    infamous for light verse and for the ?Crunchly? cartoons.

    4. In some circles, used as a punning opposite of ?crux?. ?Ah, that's the
    quux of the matter!? implies that the point is not crucial (compare tip of
    the ice-cube).

    5. quuxy: adj. Of or pertaining to a quux.