|Preach to the choir|
|Crux of the matter|
|Speak of the devil|
|An act of faith|
Theism at its most basic, is the belief in one or more gods. More modern definitions of theism suggest that the deity or deities in question must in some way impact the universe, separating theism from deism, which holds a god exists as the prime mover, but does not bother tampering with the world, if it even were able.
The belief in god(s) can be broken into a host of subsections depending on the number and the kind of the gods being postulated.
In monotheism, only one God exists. There are no other gods in the world. Most monotheists, however, tend to hold some technically untenable positions about beings like Satan or concepts like the Trinity.
Monotheism can further be divided into personal transcendent gods, and impersonal or non-transcendent gods.
A personal god is one that involves him or herself in the world, engages with the prayerful, even perhaps asking people to fear and adore him. Some well-known examples of monotheistic religions with personal gods include the three Abrahamic religions - Christianity, Islam and Judaism.
Pantheism involves the idea of God being all things. Theravada Buddhism could be said to be pantheistic or atheistic, depending on how you look at it. Atheist Wiccans often call themselves pantheistic. The difference becomes a political statement or position statement. If everything is god, then everything is the same, so what is the point of saying it is "god". Monists like Spinoza provide classical examples of true pantheists.
Panentheism the 'en' (Greek for "in") gives away the difference: there is one god, and it is present in all things, but it is at the same time, a transcendent entity. God is separate from his creation, though he is within each bit of his creation.
There are definitions for religions where only one god is worshiped by a people, but they acknowledge the presence of other Gods in the Universe.
Monolatrists acknowledge only one true god, and all others are false or evil though those other gods do exist in the world. Ancient Christianity, with its placement in and around the polytheistic Greeks was Monolatrist, describing other Gods as shadows of Satan. A well-known modern representative of monolatrism is the Church of Jesus Christ of Latter-Day Saints.
Henotheists acknowledge only one god, but admit that other gods may exist, and that there is no universally correct path, all "good" gods are equally valid. But within their own community, only the one god is worshiped or valued as "real".
Many in the Unitarian Universalist church, especially those who have come from Christianity, are henotheistic. The Baha'i religion also holds to a doctrine that could be construed as henotheistic, at least to the extent that the Abrahamic faiths are all held to teach essentially the same thing, regardless of different characteristics of their particular personifications of God.
In a polytheistic religion, several gods are worshiped as part of that religion. The pantheon of deities in such religions tend to specialise, in contrast with the ubiquitous gods of monotheistic religions. Most of human's culture's religions are polytheistic in nature, from various Native american religions, to the Classical Greeks, ancient Celtic religions, to the early Israelites. Zoroastrians hold a belief in two complementary deities or, analogously to Christianity, two complementary aspects of a single deity.