An unidentified flying object is exactly what it says on the tin: Something moving through the air which the observer can't put a name to. I've seen one... for about half a second, before my brain caught up with my eyes and said, "It's an aeroplane viewed from side on as it moves on a landing trajectory. You can't see the wings because you're exactly in line with them. The tail is the same colour as the sky".
It was hardly a thrilling scene from The X-Files. I just happened to be walking down a road that's high up in the middle of the afternoon, and looked to my left while the plane was descending. I could see something, and for a split second I could not recognise it. After my brain kicked in its logic circuits and I'd figured out what it was, and why it didn't look familiar, I waited and saw the aeroplane come into focus as it moved lower. Then I could see the detail - the tail was now visible against the hills, and the tips of the wings were outside the silhouette of the fuselage.
But wow, that's how it works: The eyes see something and the visual cortex processes it, while the brain tries frantically to work out what it is seeing. Because it's an image outside of previous experience, the brain hasn't worked out what it's seeing by the time the visual cortex has processed the image fully: Total confusion is the result until the viewer works out the optical illusion.
In this specific case, the likelihood of catching the exact right moment while passing the exact right spot on the exact right road and looking in the exact right direction is very small. Not to mention that everyone knows what an aeroplane is these days and thus can work out what they're seeing quickly if they do get lucky, so it's no wonder we don't see regular news stories about cigar-shaped flying saucers racing about Wellington harbour.
Of course, we really do hear about UFOs here, far too often. This is odd considering large nations like the United States of America probably have less (or less prominent) reports of "erratically moving lights in the sky" in the national media. Perhaps it's always a slow news day here on an island where sheep feature in the news more often than not - though not always on page three, despite what you've all heard. The news here is full of fluff pieces, which offend the sensibilities more often than not. Thankfully these days the reporters do some actual work when they hear about mysterious lights in the sky and phone up an astronomer or meteorologist to ask them what's going on.
The latest one consisted of people reporting lights moving slowly across the night sky and then disappearing. The fact that this comes at the same time as the police and coast guard are getting annoyed about sky lanterns being released on beaches - subsequently reported as flares, which means they're obligated to investigate - indicates an entirely earthly origin for these lights. I'm quite impressed that the journalists managed to resist the sensationalist urge and actually wrote it all up properly. There's hope yet for news reporting...
...at least, until they sensationalise the next Bigfoot hoax.