Unidentified flying objects (commonly abbreviated UFO) are aerial phenomena that are not readily identified. The USAF, who originally invented the term in 1952, define UFOs as only those objects remaining unidentified after scrutiny by expert investigators.
In addition, the term UFO is also often used as a synonym for alien spacecraft, though an anomaly may be classified as a UFO independently of opinion as to its origins. Because of the confusion of meanings that have become associated with UFO, some investigators instead prefer to use the broader term Unidentified Aerial Phenomena (or UAP).
The vast majority of reports are of something real, perhaps appearing anomalous, but most of these represent honest misidentifications of conventional objects such as aircraft, balloons, or astronomical objects such as meteors or bright planets.