What Is the Origin of the Term 'UFO'?

2 July is World UFO Day, commemorating the purported UFO crash on 2 July 1947, in the Roswell UFO Incident. Whether or not you’re a believer in the existence of UFOs, you might have wondered where the term UFO came from. You probably know that it stands for ‘unidentified flying object’, but what is the origin of the term and when was it first used?
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