in early Greek cosmology, either the primeval emptiness of the universe before things came into being or the abyss of Tartarus, the underworld. Both concepts occur in the Theogony of Hesiod. First there was Chaos in Hesiod's system, then Gaea and Eros (Earth and Desire). Chaos, however, did not generate Gaea; the offspring of Chaos were Erebus (Darkness) and Nyx. Nyx begat Aether, the bright upper air, and Day. Nyx later begat the dark and dreadful aspects of the universe (e.g., Dreams, Death, War, and Famine). This concept tied in with the other early notion that saw in Chaos the darkness of the underworld.

In the later cosmologies Chaos generally designated the original state of things, however conceived. The modern meaning of the word is derived from Ovid, who saw Chaos as the original disordered and formless mass, from which the maker of the Cosmos produced the ordered universe. This concept of Chaos also was applied to the interpretation of the creation story in Genesis 1 (to which it is not native) by the early Church Fathers.