Absence of belief in a particular deity, pantheon, or religious doctrine (notwithstanding belief in other deities).
Absence of belief that any deities exist (including absence of the concept of deities).
Rejection of belief that any deities exist (with or without a belief that no deities exist).
Belief that no deities exist (sometimes including rejection of other religious beliefs).
Doubt or disbelief of religious doctrines
The practice or philosophy of being a skeptic.
The doctrine that absolute knowledge is not possible
A studied attitude of questioning and doubt
A methodology that starts from a neutral standpoint and aims to acquire certainty though scientific or logical observation.