An origin myth is a type of myth that explains the beginnings of a natural or social aspect of the world. Creation myths are a type of origin myth narrating the formation of the universe. However, numerous cultures have stories that take place after the initial origin. These stories aim to explain the origins of natural phenomena or human institutions within an already existing world. In Graeco-Roman scholarship, the terms etiological myth and aition (from the Ancient Greek αἴτιον 'cause') are occasionally used to describe a myth that clarifies an origin, particularly how an object or custom came into existence.