UFO

A UFO is an unidentified, flying object. It does not mean it is a flying spaceship harbouring a lot of almond-eyed aliens; it just means it is an unidentified, flying object. A banana peel, painted blue and with pebbles glued to it becomes a very nice UFO once you've thrown it into the air. Well, unidentified to others.

Most people see UFOs all the time. They are just ignorant of the fact that they couldn't name the plane type or anything else about the UFO and act as if it was an identified flying object to them.