Short for "Unidentified Flying Object". Stereotypical depiction of an alienspacecraft originated from various description of the supposed spotting of alien spacecraft during the 1950 - 1970s "UFO craze" around the Americas.
The most common depiction of UFO are a "flying saucer", a disc-shaped spacecraft often with a glass canopy for its occupant. Though other types such as a sphere and a cigar-shaped UFO is also often depicted.
