Systems

Atheism is a belief system.

Close your mouths, put your fingers down, and hear me out.

Atheism allows me to believe in evolution, instead of an ethereal sculptor with a magical potter's wheel. It allows me to believe in gravity, as opposed to a benevolent / malevolent deity holding me down on the ground. Atheism allows me to believe in heliocentrism, instead of geocentrism. It allows me to believe that in the possibly infinite bounds of the universe, even though we haven't found extra-terrestrial life, it's extremely likely (if not certain) to exist somewhere.

Atheism allows me to believe in a host of provable theories, instead of just one crackpot hypothesis.

Atheism allows me to open up my mind to the fascinating world around me, and instead of being satisfied with a shrug, and explanation of "gawd musta done it," actually ponder the processes by which these things came to be.

Wait...

Sorry...

"Science."

Science allows me to believe these things, by providing facts, evidence, and quantifiable data, then allowing me to use my own biochemical computer to synthesize that information. Turns out all Atheism is, is a lack of belief in gods.

Oops.

Easy to confuse the two, I suppose, but there are a few easy tricks to help you distinguish between the two:

Does it rely on evidence to prove or disprove a hypothesis? It's probably science.

Is it a lack of belief in gods? It's probably Atheism.