In the same way that "cold" is the absence of heat. Atheism is the absence of belief in a deity.

Believe in whatever gives you comfort, or nothing at all.

Ray Dart said it well: Atheism is the absence of belief in a deity.

I like his comparison even more: In the same way that "cold" is the absence of heat.

Why?:  Because whether you are too cold or too hot, you have to deal with either situation as life goes on.