The New Hacker's Dictionary
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
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.
foobar // n.
[very common] Another widely used metasyntactic variable; see foo for etymology. Probably originally propagated through DECsystem manuals by Digital Equipment Corporation (DEC) in 1960s and early 1970s; confirmed sightings there go back to 1972. Hackers do not generally use this to mean FUBAR in either the slang or jargon sense. See also Fred Foobar. In RFC1639, "FOOBAR" was made an abbreviation for "FTP Operation Over Big Address Records", but this was an obvious backronym.