From The Free On-line Dictionary of Computing (19 Sep 2003) [foldoc]:
foo
<jargon> /foo/ A sample name for absolutely anything,
especially programs and files (especially scratch files).
First on the standard list of metasyntactic variables used
in syntax examples. See also bar, baz, qux, quux,
corge, grault, garply, waldo, fred, plugh,
xyzzy, thud.
The etymology of "foo" is obscure. When used in connection
with "bar" it is generally traced to the WWII-era Army slang
acronym FUBAR, later bowdlerised to foobar.
However, the use of the word "foo" itself has more complicated
antecedents, including a long history in comic strips and
cartoons.
"FOO" often appeared in the "Smokey Stover" comic strip by
Bill Holman. This surrealist strip about a fireman appeared
in various American comics including "Everybody's" between
about 1930 and 1952. FOO was often included on licence plates
of cars and in nonsense sayings in the background of some
frames such as "He who foos last foos best" or "Many smoke but
foo men chew".
Allegedly, "FOO" and "BAR" also occurred in Walt Kelly's
"Pogo" strips. In the 1938 cartoon "The Daffy Doc", a very
early version of Daffy Duck holds up a sign saying "SILENCE IS
FOO!". Oddly, this seems to refer to some approving or
positive affirmative use of foo. It has been suggested that
this might be related to the Chinese word "fu" (sometimes
transliterated "foo"), which can mean "happiness" when spoken
with the proper tone (the lion-dog guardians flanking the
steps of many Chinese restaurants are properly called "fu
dogs").
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.
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. Almost
the entire staff of what became the MIT AI LAB was
involved with TMRC, and probably picked the word up there.
Another correspondant cites the nautical construction
"foo-foo" (or "poo-poo"), used to refer to something
effeminate or some technical thing whose name has been
forgotten, e.g. "foo-foo box", "foo-foo valve". This was
common on ships by the early nineteenth century.
Very probably, hackish "foo" had no single origin and derives
through all these channels from Yiddish "feh" and/or English
"fooey".
[Jargon File]
(1998-04-16)
From Jargon File (4.4.4, 14 Aug 2003) [jargon]:
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 variables used in
syntax examples. See also bar, baz, qux, quux, 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' or `Fucked Up Beyond All Recognition'), 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 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 one was almost certainly the Mandarin Chinese word fu
(sometimes transliterated foo), which can mean "happiness" or
"prosperity" when spoken with the rising 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, then only 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.