nounpl. UFOs or UFO's
- any of a number of unidentified objects or phenomena frequently reported, esp. since 1947, to have been observed or tracked in the sky and variously explained as being atmospheric phenomena, hallucinations, misperceptions of actual objects, alien spacecraft, etc.
- a spacecraft from another planet; flying saucer
Origin of UFOu(nidentified) f(lying) o(bject)