Zo·ro·as·tri·an·ism 
(zôr′ō-ăstrē-ə-nĭz′əm)
(zôr′ō-ăstrē-ə-nĭz′əm)n.
The religious system founded by Zoroaster and set forth in the Avesta, teaching the worship of Ahura Mazda in the context of a universal struggle between the forces of light and of darkness.
Zo′ro·astri·an adj. & n.