What is the meaning of foo?

Alex Chaffee

foo means... nothing. Literally. It's the name you give something to mean "this thing has no name." It means "fill in your own variable name here."

As to the origin of the term...

From The Jargon File:

Used very generally as a sample name for absolutely anything, esp. programs and files (esp. scratch files). ...

When `foo' is used in connection with `bar' it has generally traced to the WWII-era Army slang acronym FUBAR (`F**ked 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.

From Foo Fighters FAQ:

Near the end of WWII, the U.S. Air Force patrolling German airspace encountered highly maneuverable balls of light in the area between Hagenau in Alsace-Lorraine and Neustadt an der Weinstrasse in the Rhine Valley. These unidentified flying objects came to be referred to as "Foo Fighters", or "Kraut Balls" by those who believed the objects were a secret German weapon.

See also: