Zoroastrianism: A religion from ancient Persia (Iran) that dominated that region prior to the coming of Islam but is today a small minority faith. Named for the prophet Zoroaster (or Zarathustra), whose dates are unknown, Zoroastrianism became the official religion of Persia from the third century B.C. until the seventh century A.D. It is characterized by a *dualism in which Ahura Mazda, the god of light and goodness, struggles to overcome a powerful evil spirit, although contemporary Zoroastrians claim that they are monotheists and do not necessarily see the physical world as bad, as in the ontological dualism of *Manichaeism.
Evans, C. Stephen (2010-04-28). Pocket Dictionary of Apologetics & Philosophy of Religion (p. 125). Intervarsity Press. Kindle Edition.
Polytheism: The English equivalent of the Greek word meaning πολυς and θεος is, many god(s). This is the belief system that teaches there are more than one God. A plurality of distinct and separate deities or a pantheon of gods and goddesses exists. However, polytheists do not necessarily worship all deities equally, but they tend to particularize one god as a main god over many other gods and goddesses. In this sense, they can be more Henotheists, differentiating one deity as the main one for worshiping. “Polytheism is distinguished from theism, also called monotheism, on the basis of polytheism’s claim that divinity, while personal and distinguished from the universe, is many rather than one.” It is also contrasted with pantheism, though these two doctrines are embraced side by side in the same religious traditions in the East. All other religious beliefs in the world are overwhelmingly polytheistic with the exception of Judaism, Christianity, and Islam. Hinduism, Mahayana Buddhism, Confucianism, Taoism, and Shintoism in the East are characterized as polytheism.
 Walter A. Elwell, Evangelical dictionary of theology (Grand Rapids, Mich.: Baker Book House, 1984), 861. Print.
Theism: The term theism comes from Greek theos (Θεος) meaning God. The term refers to the belief that there is a God, or there are (many) gods who have direct or personal relationship to the universe or with human beings. Theism, in general, relates to the theory of the nature of God that is more agreeing to the most religious traditions. So, “the theistic conception of divinity can be polytheistic, that is, that there are many gods, or it can be monotheistic, that is, it can limit the conception of divinity to one God, as is the case in the Judeo-Christian-Islamic traditions”. However, the term used, in particular, sense refers to the monotheistic nature of God as a person who is infinite in his power, knowledge and actively governing the universe.
 Popkin, Richard H., and Avrum Stroll. “Philosophy of Religion.” Philosophy Made Simple,. New York: Made Simple ; Distributed to the Book Trade by Garden City , Garden City, N.Y., 1993. 176. Print.