Within aviation and specifically military aviation, "UFO" means exactly what it says on the tin, an object that is airborne (flying) but has not been identified

Within aviation and specifically military aviation, "UFO" means exactly what it says on the tin, an object that is airborne (flying) but has not been identified to be a known craft type by radio signals or visual recognition. That's all. It doesn't imply anything about what it is, only what it isn't, namely identified. There are tons of these on radar, HF etc all the time.