According to Me
According to Miriam Webster
1. a disbelief in the existence of a deity
2. the doctrine that there is no deity
According to Oxford
Disbelief or lack of belief in the existence of God or gods.
According to Wikipedia
Atheism is, in the broadest sense, the absence of belief in the existence of deities. Less broadly, atheism is the rejection of belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities.
Atheism is contrasted with theism, which, in its most general form, is the belief that at least one deity exists.
Origin and Etymology of atheism
Middle French athéisme, from athée atheist, from Greek atheos godless, from a- + theosgod