technically, anything that's in the sky qualifies as "unidentified flying object" if you don't know what it is.
rare species of bird? UFO. type of plane you've never seen before? UFO. probably a weather balloon but you're not that much into meteorology? you guessed it. UFO.
@anarchiv technically a person who leaps out of an airplane at random is a UFO, parachute or otherwise. flying is just falling in a different direction to straight down after all.
@Nine There were three people on this airplane and we don't know which one bailed... UFO
@Nine @anarchiv a flying object is just a falling object that hasn't collided with the planet yet.