Nontheism is a term that covers a range of both religious and nonreligious attitudes characterized by the absence or rejection of theism or any belief in a personal god or gods. Invented originally as a synonym for secularism (see below),^{[dubious – discuss]} it has become an umbrella term for summarizing various distinct and even mutually exclusive positions united by a naturalist approach,^{[dubious – discuss]} such as agnosticism, skepticism, and atheism. It is in use in the fields of Christian apologetics and general liberal theology^{[disambiguation needed ]}. Sometimes used synonymously with the term atheism, it can also include positions of belief in a non-personal deity, such as deism and pantheism.

Nontheism can be expressed in a variety of ways. Strong or positive atheism is the positive belief that a god does not exist. Someone who does not think about the existence of a deity may be termed a weak or negative atheist, or more specifically implicitly atheist. Other, more qualified types of nontheism are often known as agnosticism: strong or positive agnosticism is the belief that it is impossible for humans to know whether or not any deities exist. It is a more precise opinion than weak or negative agnosticism, which is the belief that the existence or nonexistence of any deities is unknown but not necessarily unknowable. Philosopher Anthony Kenny distinguishes between agnostics, who find the claim "God exists" uncertain, and theological noncognitivists, who consider all discussion of God to be meaningless. Some agnostics, however, are not nontheists but rather agnostic theists.