A UFO or unidentified flying object is an apparition in the sky which exhibits motility or impermanence while not being readily identifiable.

Many people claim UFOs are extraterrestrial aircraft but the majority of scientists say there is no definitive evidence to support that supposition People tend to believe all sorts of non-scientific and paranormal concepts and to accept this belief without proof. A prevalent belief is that aliens from some other cosmic body have visited the earth, though there is no direct proof of such an event. Many see this belief as deriving from the prevalence of science fiction in literature, films, and television and from anxiety brought about during the Cold War era, but in fact some belief in alien beings can be found throughout history, though identifying these interlopers as aliens from another planet is more common today than it was in the past. The publicity of encounters with UFOs started in the late 1940's. There had been reports before that time, but they had not received much exposure by the media. It all started in 1947.

One day Kevin Arnold, who was flying his single engine plane, reported that he had seen objects flying around that could not be explained. He estimated their speed to be three times what was possible at that time. He described their motion was similar to that of a saucer skipping across water. The term flying saucer was born. Almost fifty percent of Americans, according to recent polls, believe that UFOs.