A theist is a person who believes in one or more gods or deities. Theism is the corresponding philosophical position. Theism does not denote any particular religious view, but all religions with any number of gods are by definition theistic religions. Conversely, religions without a necessary god (such as Buddhism) are atheistic religions.
Theism differs from deism in that theism is a narrower belief in divinities that are immanent in the world and can interact with it. Generally, monotheistic gods are omniscient, omnipresent, and omnipotent.