What term describes a person who does not believe in any deity?

The correct term for a person who does not believe in any deity is "atheist." An atheist holds the view that there is no god or gods, differing significantly from individuals who might believe in one or more deities.

Understanding the other terms provides further context. A theist is someone who believes in one or more gods, while an agnostic is a person who remains unsure or claims that the existence of a deity is unknown or unknowable. Humanism, on the other hand, is a philosophical stance that emphasizes human value and agency, often without a focus on religious beliefs, but it does not specifically address belief in deities.

Thus, "atheist" is the appropriate term as it directly specifies a lack of belief in any god, distinguishing it from the other concepts that either represent belief or uncertainty about deity existence.