Atheism is, in the broadest sense, 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.
Also included in this category is Agnosticism
Agnosticism is the view that the existence of God, of the divine or the supernatural is unknown or unknowable. Another definition provided is the view that “human reason is incapable of providing sufficient rational grounds to justify either the belief that God exists or the belief that God does not exist.”