foo bar is very often used in computer programming, used to declare a (temporary) variable.
Most probably, "foo" and "bar" came from "foobar," which in turn had its origins in the military slang acronym FUBAR. The most common rendition is "Fucked Up Beyond All Recognition"

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

A common term found in unix/linux/bsd program help pages as space fillers for a word.
Or, can be used as a less intense or childish form of fubar.

The phonetic pronounciation of the acronym "F.U.B.A.R." which stands for "Fucked Up Beyond All Recognition"

1) A placeholder used in programming, and other computer uses

2)Short for the music player foobar2000, named after the above definition

A slang term meaning "fucked up beyond all recognition." The saying was used primarilly in programing and originated as fubar, but for political correctness it was changed to foo bar.

Foo and bar also often represent variables.

1) What basement dwellers say when they can't come up with anything. The writer prefers meow. (see also: swedish chef)

2) A very configurable media player. There is that form vs function prob though, so it takes a month to figure out the volume control, and you'll still bitch it out all the time. Can play and rip at the same time, which is nice. (aka foobar2000 foobar2k fb2k fb)