UFO stands for Unidentified Flying Object. It refers to any aerial phenomenon that cannot be immediately identified by the observer. The term is commonly associated with sightings of objects in the sky that may be thought to be extraterrestrial spacecraft, although many UFO sightings have been later explained as conventional phenomena such as aircraft, balloons, or atmospheric conditions. The intrigue surrounding UFOs has led to various investigations, cultural phenomena, and conspiracy theories, but by definition, a UFO simply denotes an object in the sky that remains unidentified at the time of observation.