Just saw this, that’s on me. I made the assumption people knew it as it’s frequently used with the topic. UAP was Unidentified Aerial Phenomenon, but was recently changed officially to Unidentified Anomalous Phenomenon to broaden the scope of things that could fit into the area of study. Another reason is that some agencies were dodging the law that requires reporting given the definition was specific to things in the air, and not space or water.