A religious system with Christian, Gnostic, and pagan elements, founded in the 3rd cent. a.d. and widespread in the Roman Empire and Asia until the 5th cent. (surviving until the 13th cent.), based on the supposed primeval conflict between light and darkness, and representing Evil as coeternal with God; (more generally) dualism. (OED)
dualism. 3. A theory or system of thought which recognizes two independent principles. spec.: (a) (Philos.) the doctrine that mind and matter exist as distinct entities; opposed to idealism and materialism; (b) the doctrine that there are two independent principles, one good and the other evil . . .
Wikipedia article on Manichaeism