UFO just means any flying object that is unidentified. A helium balloon blowing around in the wind that reflects sunlight in a way that looks weird to you on the ground could be a UFO, and has been reported as such thousands of times. A test flight by the air Force, a drone, a spy plane, a meteorite, all kinds of things.

There's no intelligent life form secretly visiting earth and accidentally dropping their amazing technology anywhere. This is just the modern equivalent of "I can't immediately explain this, it must be supernatural!" AKA religion. Please find something better to do with your time.