UFO

A UFO (Unidentified Flying Object) is defined as being any unexplained moving object observed in the sky, especially one assumed by some observers to be of extraterrestrial or interdimensional, "alien", origin. The first use of the term, as acronym or long form, is believed to have been in 1953 AD.

Similar apparent vehicles and phenomena are seen over and under the water in oceans, seas and lakes. These phenomena or vehicles are known as USOs, Unidentified Submerged Objects.