UFO is an acronym for Unidentified Flying Object. This acronym is used when talking about aliens. Every craft that’s in the sky is accounted for, either by satellite, radar, or it’s a commercial flight that has been noted. It’s hard for any object in the sky to be unidentified.
This is why alien sightings are classified as UFOs. Because they don’t appear on any surveillance, but people still see them. So, the governments can’t identify them, but people have seen them, or claim to have seen them. There was No proof ever that UFOs really exist, which is why they still remain unidentified to this day.