The Full form of UFO is Unidentified Flying Object. It refers to a body or a flying object in the sky that does not known or belong to our world, e.g. it cannot be identified as a known object (missile, airplane, etc) or a natural phenomenon. UFO is basically related to aliens and unseen extraterrestrial life from other planets. After investigation, most UFOs are identified as conventional objects or phenomena. The term is widely used for claimed observations of extraterrestrial spacecraft.
The term UFO was first used in 1953 by United States Air Force (USAF) to indicate any mysterious flying body or object that is not supposed to be capable of flying. USAF defined UFO as any airborne object which by its aerodynamic and performance does not resemble any known missile, aircraft, etc. It is often referred to as flying discs in the late 1940s and during 1950s. In 2017, the maximum number of sightings of the UFO has been reported.
Since the National UFO Reporting Center began keeping the record of UFOs in the last 112 years, there have been more than 100,000 UFO sightings worldwide. Out of these huge numbers of sightings, the majority were seen in the United States. Most of these UFO sightings can be explained as fireworks, airplanes, and comets.