This article is about the aerial phenomenon. For the rock band, see Foo Fighters.

The name foo fighter was coined by Allied aircraft pilots in World War II for mysterious aerial phenomena, such as glowing ball lightning seen in the skies over Germany. Originally used as a semi-derogatory reference to Japanese fighter pilots (known for erratic flying and extreme maneuvering), it became a catch phrase for fast moving, erratically flying objects (such as UFOs). It was thought at the time that they might be some Nazi secret weapon, but the Germans were just as mystified by the phenomenon. It could very likely be incidences of floating plasma that have been found in many areas of the world, of which science is still far from understanding. The "foo fighter" was a secret Luftwaffe aircraft nicknamed the "feuerfighter" by the Germans. It was highly confidential, and was disk shaped. Some sightings of foo-fighters may have been night-sightings of the German Me163 Komet rocket-plane.

The term probably originated in the surrealistic comic strip Smokey Stover. Smokey, a firefighter, was fond of saying "Where there's foo there's fire." A Little Big Book titled Smokey Stover the Foo Fighter was published in 1938.

Some have thought that the term refers to Kung fu ("kong foo") fighting, because of its wild, erratic movements of these objects. The term Kung fu was however little known in the English language until the late 1960s when it became popular because of the Hong Kong films and later also the television series: before that it was referred to primarily as "Chinese Boxing".

See also Foo bar.