- An extraterrestrial is a being coming from a world other than Earth, whose true existence has not yet been proved.
- Popular representations of extraterrestrials often make them be little skinny humanoids with a large skull, wide black eyes and a green or grey skin.
- (metaphorical) An extraterrestrial can also be so an uncommon person that ordinary people think he or she cannot be from Earth.
- Joseph von Neumann had so exceptional intellectual abilities that his neighbouring considered him an extraterrestrial.
- Extraterrestrial can be applied to anything not coming from the Earth or not belonging to the Earth.
- Meteorites falling on the Earth's ground come from outer space : they are extraterrestrial objects.