Atheism, lack of belief in God or gods?

That specific term "lack of belief in God or gods" I see mentioned often on here when atheists are defining atheism. Although I've yet to see this exact term mentioned in any of the definitions I've looked at, at least not in the top 3 anyway. Is this a term that describes weak atheism? Could it not also be applied to agnostics? Is it a term for agnostic-atheism rather than atheism?