> Where "Foo" and "Bar" Came From

The most commonly cited origin traces "foo" and "bar" back to military slang from WWII - specifically FUBAR ("[fouled] up beyond all recognition") - which filtered into early hacker culture (MIT's Tech Model Railroad Club and, later, ARPANET documentation) as a placeholder pair for "some arbitrary thing" and "some other arbitrary thing." The etymology is debated in the details, but the FUBAR connection is the explanation the Jargon File itself settles on. Nobody remembers who used it first in code; everybody's used it since.