Foo Fighter

Foo Fighter \FOO-FAHY-ter\ , noun;
1. Any unidentified flying object described as a ball of fire or light

So, that band didn't come up with this one on their own?
Foo fighter is first attested in 1945, though it's likely a bit older since it's US military slang. It comes from a nonsense word created by American cartoonist Bill Holman in his strip 'Smokey Stover.'

Here's a comic from the 1930's which includes the word foo:

Source: Smokey-Stover.com