As stated earlier. UFOs exist. If you see a flying object which you cannot identify, be it a weather balloon or a secret test verion of a stealth craft, then it is, to you, a UFO.

Of course, if a spaceship does/will/has appeared in our sky, then that is what is normally accepted as a UFO.

However, in the past, (Such as in the film/radio-prog/book "The War of the Worlds") Mars was seen to emit green beams, the trails of spaceships, which landed on Earth, containing Martians. These, by very definition, are NOT UFOs. They have been identified.

Nigel