Answer: Foo Fighters

If you’re not a military history buff, there’s likely one thing, and one thing alone, that you think of when you hear the term “Foo Fighters”—the band, lead by former Nirvana drummer Dave Grohl, best known for hits like “Learn to Fly”, “Monkey Wrench”, and “My Hero”.

Grohl’s inspiration for the name wasn’t just pairing a nonsensical word with “fighters”, but an existing slang from mid-century military history. In World War II, Allied pilots stationed in Europe and the Pacific theaters began describing unidentified flying objects and phenomenon they witnessed as “foo fighters”. The usage is widely believed to have started with radar operator Donald J. Meiers, in the U.S. 415th Night Fighter Squadron, to describe what they had seen. Meiers, in turn, had borrowed the term “foo” from cartoonist Bill Holman, who used the made up word in puns within his comic strips.

At the time, the soldiers believed the “foo fighters” to be some sort of enemy weaponry they were unfamiliar with, and potentially, top secret German experiments. Today, however, the more accepted explanation is that the plane crews were witnessing atmospheric events like ball lightning, electrostatic phenomena (similar to St. Elmo’s fire), electromagnetic phenomena, or simply reflections of light from ice crystals.