foo /foo/ 1. interj. Term of disgust. 2. [very common] Used very
   generally as a sample name for absolutely anything, esp. programs and
   files (esp. scratch files). 3. First on the standard list of
   {metasyntactic variable}s used in syntax examples. See also {bar},
   {baz}, {qux}, {quux}, {corge}, {grault}, {garply}, {waldo}, {fred},
   {plugh}, {xyzzy}, {thud}.

   When `foo' is used in connection with `bar' it has generally traced to
   the WWII-era Army slang acronym {FUBAR} (`Fucked Up Beyond All Repair'),
   later modified to {foobar}. Early versions of the Jargon File
   interpreted this change as a post-war bowdlerization, but it it now
   seems more likely that FUBAR was itself a derivative of `foo' perhaps
   influenced by German `furchtbar' (terrible) - `foobar' may actually have
   been the _original_ form.

   For, it seems, the word `foo' itself had an immediate prewar history
   in comic strips and cartoons. The earliest documented uses were in the
   "Smokey Stover" comic strip published from about 1930 to about 1952.
   Bill Holman, the author of the strip, filled it with odd jokes and
   personal contrivances, including other nonsense phrases such as "Notary
   Sojac" and "1506 nix nix". The word "foo" frequently appeared on license
   plates of cars, in nonsense sayings in the background of some frames
   (such as "He who foos last foos best" or "Many smoke but foo men chew"),
   and Holman had Smokey say "Where there's foo, there's fire".

   According to the Warner Brothers Cartoon Companion
   (http://www.spumco.com/magazine/eowbcc/) Holman claimed to have found
   the word "foo" on the bottom of a Chinese figurine. This is plausible;
   Chinese statuettes often have apotropaic inscriptions, and this may have
   been the Chinese word `fu' (sometimes transliterated `foo'), which can
   mean "happiness" or "prosperity" when spoken with the proper tone (the
   lion-dog guardians flanking the steps of many Chinese restaurants are
   properly called "fu dogs"). English speakers' reception of Holman's
   `foo' nonsense word was undoubtedly influenced by Yiddish `feh' and
   English `fooey' and `fool'.

   Holman's strip featured a firetruck called the Foomobile that rode on
   two wheels. The comic strip was tremendously popular in the late 1930s,
   and legend has it that a manufacturer in Indiana even produced an
   operable version of Holman's Foomobile. According to the Encyclopedia of
   American Comics, `Foo' fever swept the U.S., finding its way into
   popular songs and generating over 500 `Foo Clubs.' The fad left `foo'
   references embedded in popular culture (including a couple of
   appearances in Warner Brothers cartoons of 1938-39; notably in Robert
   Clampett's "Daffy Doc" of 1938, in which a very early version of Daffy
   Duck holds up a sign saying "SILENCE IS FOO!") When the fad faded, the
   origin of "foo" was forgotten.

   One place "foo" is known to have remained live is in the U.S. military
   during the WWII years. In 1944-45, the term `foo fighters' was in use by
   radar operators for the kind of mysterious or spurious trace that would
   later be called a UFO (the older term resurfaced in popular American
   usage in 1995 via the name of one of the better grunge-rock bands).
   Because informants connected the term directly to the Smokey Stover
   strip, the folk etymology that connects it to French "feu" (fire) can be
   gently dismissed.

   The U.S. and British militaries frequently swapped slang terms during
   the war (see {kluge} and {kludge} for another important example) Period
   sources reported that `FOO' became a semi-legendary subject of WWII
   British-army graffiti more or less equivalent to the American Kilroy.
   Where British troops went, the graffito "FOO was here" or something
   similar showed up. Several slang dictionaries aver that FOO probably
   came from Forward Observation Officer, but this (like the
   contemporaneous "FUBAR") was probably a {backronym} . Forty years later,
   Paul Dickson's excellent book "Words" (Dell, 1982, ISBN 0-440-52260-7)
   traced "Foo" to an unspecified British naval magazine in 1946, quoting
   as follows: "Mr. Foo is a mysterious Second World War product, gifted
   with bitter omniscience and sarcasm."

   Earlier versions of this entry suggested the possibility that hacker
   usage actually sprang from "FOO, Lampoons and Parody", the title of a
   comic book first issued in September 1958, a joint project of Charles
   and Robert Crumb. Though Robert Crumb (then in his mid-teens) later
   became one of the most important and influential artists in underground
   comics, this venture was hardly a success; indeed, the brothers later
   burned most of the existing copies in disgust. The title FOO was
   featured in large letters on the front cover. However, very few copies
   of this comic actually circulated, and students of Crumb's `oeuvre' have
   established that this title was a reference to the earlier Smokey Stover
   comics. The Crumbs may also have been influenced by a short-lived
   Canadian parody magazine named `Foo' published in 1951-52.

   An old-time member reports that in the 1959 "Dictionary of the TMRC
   Language", compiled at {TMRC}, there was an entry that went something
   like this:

  FOO: The first syllable of the sacred chant phrase "FOO MANE PADME
  HUM."  Our first obligation is to keep the foo counters turning.
  
   (For more about the legendary foo counters, see {TMRC}.) This
   definition used Bill Holman's nonsense word, only then two decades old
   and demonstrably still live in popular culture and slang, to a {ha ha
   only serious} analogy with esoteric Tibetan Buddhism. Today's hackers
   would find it difficult to resist elaborating a joke like that, and it
   is not likely 1959's were any less susceptible. Almost the entire staff
   of what later became the MIT AI Lab was involved with TMRC, and the word
   spread from there.


Source: The Jargon File