There are real atheists (aka normal people) and there are fake atheists (aka fucktards).

"Is atheism the belief that a deity isn't real?"

Atheism is an acceptance of reality. Reality is not a belief.

I'm 100% certain magic god fairies and Easter Bunnies are not real. This is not a belief. This is reality.

The word "belief" is for feeble-minded cowards who don't want to throw out their childish everything-is-magic fantasy world.

One more thing: Fake atheists who say "lack of belief" have my contempt. Atheism is not a lack of belief. Atheism is 100% certainty that magic fairies are not real. Do these fucktards say they have a lack of belief in Easter Bunnies? Probably not. Apparently they think magic god fairies are more likely to be real than magical rabbits. These people are not real atheists. I call them "idiots".