The operative word is “unidentified.”
Just because you can’t tell what it is doesn’t mean it’s aliens.
It's odd...or perhaps not...that UFO has become interchangeable with "alien spacecraft."
Is it an object? Yes. Is it flying? Yes. Can you identify it? No.
Then it is an unidentified flying object. No more, no less.
Precisely...The “UFO” acronym has lost its original meaning to designate a sighting of an object in the sky that was not identifiable as to type or origin, and has taken on an immediate popular association with extraterrestrial beings and their craft...Little green men has become the default explanation for anything unidentified/able in the sky...
The Earth may well have been visited by alien beings and may be still, and it’s sometimes their aircraft being sighted...But so far, aside from grainy still images, and shaky camera phone video, there just isn’t any real evidence, and little if any concrete proof of alien presence being made public, and Ufology remains more a religion than a science for the true believers...