Theism: The belief in the existence of one or more deities. There are many manifestations of theism. One of the most common is monotheism-the belief in only one deity(or, in the case of Christianity, one deity in manifestations). Another common one is polytheism-the belief in more than one deity(Greek/Roman mythology and Hinduism come to mind). There is pantheism-the belief that the entire universe and everything within make up god. There are other forms as well.

Theist: One with a belief in one or more deities. For every type of theism, assuming it has a following, there is an associated type of theist(monotheist, polytheist, pantheist, etc).

Religion: A division more clearly specifying the type of theism. The type of religion narrows down the beliefs of the theists, yet it is still broad. Religion unites theists in the general aspects of their beliefs. A few prominent religions are Christianity, Islam, and Judaism.

Denomination(or sect): A division of religion more clearly specifying the type of theism. A denomination unites believers with the details of their beliefs. Examples of denominations are Baptist, Mennonite, Evangelical, Methodist, Presbyterian, Catholic, etc.

Atheism: The lack of belief in one or more deities. This lack of belief can take a range of forcefulness from a general not believing in any gods(known as "Weak Atheism", it is the basic and most common form of atheism) to a distinct belief that no gods exist(known as "Strong Atheism", it is the most vocal and most commonly known form of atheism). As you can see from the etymology of the word("A"[without]+"Theism"[belief in one or more deities]) that atheism in general is a lack of theism.

Atheist: One who lacks a belief in the existence of deities. Anyone who is not a theist is an atheist. As with atheism, atheists range in forcefulness from "Weak Atheists" to "Strong Atheists".

Agnosticism: The belief that it is impossible to know if any deities exist. Agnosticism is not, as is it is commonly misconstrued, an alternative to theism and atheism(you either believe in one or more deities, or you do not; there is no middle), but rather a modifier for the terms. There is both Agnostic Theism and Agnostic Atheism.

Agnostic: One who believes it is impossible to know if one or more deities exist. As with Agnosticism, an Agnostic is either an Agnostic Theist or an Agnostic Atheist. Most people who classify themselves as "Agnostic" without specifying the type are Agnostic Atheists.

Apostate: One who has left a religion.

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"My beloved put in his hand by the hole of the door, and my bowels were moved for him."- Song of Solomon 5:4