Which term refers to the belief that there is no proof of a deity's existence?

The term that refers to the belief that there is no proof of a deity's existence is atheism. Atheism is characterized by a rejection of belief in the existence of God or gods, often based on the lack of evidence to support such a belief. Atheists may argue that without concrete proof or observable evidence for the existence of a deity, it is more rational to refrain from belief.

Agnosticism, though similar, is distinct in that it holds the view that the existence or non-existence of any deity is unknown or unknowable. While agnostics may lean towards skepticism or doubt, they do not outright deny the possibility of a deity's existence; instead, they contend that such questions may be beyond human understanding.

Theism is the belief in one or more deities, which does not align with the assertion of no proof for a deity's existence. Spiritualism, on the other hand, generally involves the belief that spirits of the dead can communicate with the living, often implying some form of spiritual belief that may or may not involve a deity.

Thus, the most accurate term describing the belief in no proof of a deity's existence is atheism.