theism is the religious belief that at least one god exists while rejecting the existence or importance of polytheistic gods or goddesses. in a broader definition it can also be the belief in god or gods in general, including all types of god-belief. polytheism is the belief in several gods, while monotheism is the belief in just one god. for example, a theistic religion is christianity. the opposite to a theist is an atheist. an atheist is a person who denies or disbelieves the existence of a supreme being or beings.