"UFO" means precisely what it always means: A motte-and-bailey term which denotes any unidentified flying object up until someone wants to be flashy, at which point it's aliens in cutting-edge military technology spying for Them. Are they space aliens? Well, will space aliens get you to click the damn link?

It's tiresome. It's a massive game of "I don't know, therefore my theory is correct" being played by, or on, people who don't quite get that ignorance isn't evidence in favor of their pet theory.