10. The 'Foo Fighters'
Most people may know the 'Foo Fighters' as a Seattle rock band founded by Nirvana drummer Dave Grohl, but the term was actually first used by Allied aircraft pilots during the Second World War to describe unidentified flying objects (UFOs).
Originally coined by the US 415th Night Fighter Squadron to report any UFO sightings during World War II, it became formal military language from November 1944. As well as referring to UFOs spotted over the European and Pacific battlefields, the term could also be applied to any mysterious aerial phenomena - such as the strange objects flying past the planes in the picture above.
Military personnel from the Western Powers often assumed foo fighters were secret Nazi weapons that were either spying on them or planting some sort of explosive device near Allied strongholds. However, a scientific investigative group named the Robertson Panel met in January 1953 in order to determine exactly what these supposed UFOs were - and returned some findings, although none were conclusive. They determined that one possible explanation could be St Elmo's fire, a weather phenomenon whereby a strong electric field in the atmosphere illuminates objects and makes them look like a glowing ball of light. Another theory is that "ball lightning" was the cause - this is when luminous, spherical objects during a thunderstorm last longer than lightning bolts and remain around in the atmosphere.
Author Renato Vesco remained convinced that it was a Nazi secret weapon, however, and claimed foo fighters were a ground-launched automatically-guided jet-propelled flak mine name the "Feuerball", although nothing was ever proven. It is unlikely that a definitive explanation will ever be found...