A common term we all hear in regards to alien space craft is UFO, standing for Unidentified Flying Object.
Essentially, anything that you see in the air, but do not recognize is a UFO. A frisbee, a baloon, a plane, a satellite. UFO therefore is a very misleading term. Of course we are all seeing unidetified air craft eevryday.
People snap a picture of a flying disc or triangle and call it a UFO. UFO reseraches show us the picture, and as the public if we think it is a ufo. If neither they nor we know what it is, then OFR COURSE it's a ufo!
IAC or UAC is a much better term. It stands for Identified/Unidentified Alien Craft. The next time you see a picture of a ufo, keep this in mind. Before the Stealth bomber was declassified, IT was a UFO technically.
When I see a picture of a UFO, I try to distinguish between whether it is man made, alien made, a collaberation of the two, or fake.