The average theologian (there are exceptions, of course) uses 'atheist' to mean a person who denies the existence of a God. Even an atheist would agree that some atheists (a small minority) would fit this definition. However, most atheists would stongly dispute the adequacy of this definition. Rather, they would hold that an atheist is a person without a belief in God. The distiniction is small but important. Denying something means that you have knowledge of what it is that you are being asked to affirm, but that you have rejected that particular concept. To be without a belief in God merely means that yhe term 'god' has no importance or possibly no meaning to you. Belief in God is not a factor in your life. Surely this is quite different from denying the existence of God. Atheism is not a belief as such. It is the lack of belief.

When we examine the components of the word 'atheism,' we can see this distinction more clearly. The word is made up of 'a-' and '-theism.' Theism, we will all agree, is a belief in a God or gods. The prefix 'a-' can mean 'not' (or 'no') or 'without.' If it means 'not,' then we have as an atheist someone who is not a theist (i.e., someone who does not have a belief in a God or gods). If it means 'without,' then an atheist is someone without theism, or without a belief in God.

[Gordon Stein (Ed.), "An Anthology of Atheism and Rationalism", p. 3.