Atheism is, in a broad sense, the rejection of belief
Belief is the psychological state in which an individual holds a proposition or premise to be true.-Belief, knowledge and epistemology:The terms belief and knowledge are used differently in philosophy....

 in the existence of deities
Existence of God
Arguments for and against the existence of God have been proposed by philosophers, theologians, scientists, and others. In philosophical terms, arguments for and against the existence of God involve primarily the sub-disciplines of epistemology and ontology , but also of the theory of value, since...

. In a narrower sense, atheism is specifically the position that there are no deities
A deity is a recognized preternatural or supernatural immortal being, who may be thought of as holy, divine, or sacred, held in high regard, and respected by believers....

. Most inclusively, atheism is simply the absence of belief that any deities exist.
Atheism is contrasted with theism
Theism, in the broadest sense, is the belief that at least one deity exists.In a more specific sense, theism refers to a doctrine concerning the nature of a monotheistic God and God's relationship to the universe....

which in its most general form is the belief that at least one deity exists.

The term atheism originated from the Greek (atheos), meaning "without god", which was applied with a negative connotation to those thought to reject the gods worshipped by the larger society.

The inhabitants of the earth are of two sorts: Those with brains, but no religion, And those with religion, but no brains.


A little philosophy inclineth man's mind to atheism; but depth in philsophy bringeth men's minds about to religion.

Francis Bacon|Sir Francis Bacon, Essays, 16, "Of Atheism"

Atheism leaves a man to sense, to philosophy, to natural piety, to laws, to reputation; all which may be guides to an outward moral virtue, though religion were not; but superstition dismounts all these, and erecteth an absolute monarchy, in the minds of men.

Sir Francis Bacon, Essays, 16, "Of Superstition"

ATHEISM: A godless religion that retains all the dogmatic posturing of the faiths it so confidently denies, with few of the consolations.

Rick Bayan|Rick Bayan, The Cynic's Dictionary, unidentified ISBN/edition, unidentified chapter/page