I hate seeing it used that way on HN though because it actively undermines meaty discussion of objective data and promotes the treatment of articles about objective data as click-bait, like it's the "hot sheets" of Men in Black -- like HN is a place to take seriously the wildest conspiracy theories with no real basis.
I thought UAP stands for "unidentified aerial/aerospace phenomenon". Anyway it's better than UFO because it primes you for the fact that many "UFOs" are not flying at all. Many are stars, lights of all kinds, or artifacts of the the recording equipment.
(From the internet: UAP stands for "unidentified anomalous phenomena.")
It's flying saucers carrying aliens from another planet that's controversial and up for debate.