Doubt, uncertainty, or scepticism regarding the existence of a god or gods.
Doubt, uncertainty, or scepticism regarding any subject of dispute.
The view that absolute truth or ultimate certainty is unattainable, especially regarding knowledge not based on experience or perceivable phenomena.
The view that the existence of God or of all deities is unknown, unknowable, unproven, or unprovable.
An absence (or rejection) of belief, especially religious belief