Atheism, in the broadest sense, is an absence of belief in the existence of deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities.

What is considered a non-believer?

: a person who does not believe in something (such as a religious belief or a scientific idea about how something happens or could happen) See the full definition for nonbeliever in the English Language Learners Dictionary.

What is non-believer in religion?

noun. a person who lacks belief or faith, as in God, a religion, an idea, or an undertaking.