For other uses, see Unidentified flying object (disambiguation).
"UFO" redirects here. For other uses, see UFO (disambiguation).
"ufo" redirects here. For the genus of gall-wasps, see Ufo (genus).
An unidentified flying object or UFO, is defined as a perceived object in the sky, not identifiable by standard criteria. Most UFOs are later identified as conventional objects or phenomena. The term is widely used for claimed observations of extraterrestrial craft.