Definitions for "Unidentified Flying Object"
The general term given to any aircraft of unknown origin. A wide variety of UFOs have been reported, with disk, cigar and triangle shapes being the most common.
Inexplicable sightings of lights, objects, or anomalous airborne craft in the sky, often perceived as being "extraterrestrial" in origin.
an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins