In Greek mythology, Chaos (Xάος) or Khaos is the original state of existence from which the first gods appeared. In other words, the dark void of space. It is made from a mixture of what the Ancient Greeks considered the four elements: earth, air, water and fire. For example, when a log is burned, the flames were attributed to the fire in it, the smoke the air in it, the water and grease that come from it were supposed to be the water, and the ashes left over were the earth. In Greek it is Χάος, which is usually pronounced similarly to "house" (Coinè) or "cows" (Attic), but correctly in ancient Greek as ['kha.os]; it means "gaping void", from the verb χαίνω "gape, be wide open, etc", Proto-Indo-European *"ghen-", *"ghn-"; compare English "chasm" and "yawn", Old English geanian = "to gape".

Ovid, in his Metamorphoses, described Chaos as "rather a crude and indigested mass, a lifeless lump, unfashioned and unframed, of jarring seeds and justly Chaos named". From that, its meaning evolved into the modern familiar "complete disorder".

Chaos features three main characteristics: it is a bottomless gulf where anything falls endlessly. This radically contrasts with the Earth that emerges from it to offer a stable ground. it is a place without any possible orientation, where anything falls in every direction. it is a space that separates, that divides: after the Earth and the Sky parted, Chaos remains between both of them.