First off, the word stands for "Unidentified Flying Object". Nothing in that forces it to be from another world. Anything that happens to be flying through the air that you cannot explain is a U.F.O. Meaning, if someone throws a plate and you see it and don't realize it is a plate, then to you it is an unidentified flying object. Plus, it says "unidentified" the title. If you know it's an alien spacecraft, then it's not a U.F.O. anymore. It's an alien spacecraft by your identification. U.F.O.s remain unidentified. That's why we call them U.F.O.s. We don't know what they are!
The sad thing is that if I were to go out and say "I saw a U.F.O. once", people would automatically think I'm crazy or they would think I'm talking about aliens. I've never seen aliens and I'm not dense enough to automatically assume that something in the sky that I see and can't explain is from another planet. There's just no way to know whether something is alien without actually being told it is by the theoretical aliens inside, or actually studying the object to determine if it is. What really sucks about this notion is that any hope to have serious, legit, and well funded research into the unexplained is lost because the people who would be funding such a project are lambasted with news of aliens and little green men, rather than simply told "we don't know what it is and we want to find out". Maybe if more people approached it from a simple "we don't know" approach we'd see more research into the bizarre things we see in the sky. Are they aliens or are they a government experiment, or neither? What if we found out they were weird visual anomalies left over from some previous human time when we were ruled, more or less, by fear?
So, the next time someone says "I saw a U.F.O.", ask them if they mean aliens or if they mean something unexplained. Probably most of them will go with the alien side, but maybe you'd find someone that used the term for its original purpose.
(Don't click the read more, there isn't any more after this!)