Just for snicks, I'll leave this here.
Quote:
UFO (yf-)
n. pl. UFOs or UFO's
An unidentified flying object.
http://www.thefreedictionary.com/UFO
Quote:
UFO [yoo-ef-oh or, sometimes, yoo-foh]
noun, plural UFO's, UFOs.
any unexplained moving object observed in the sky, especially one...