No, atheism is not a belief system, nor is it a religion.

It works like this:

If someone is not political, then they are apolitical.
If something is not symmetrical, then it is asymmetrical.
If something is not typical, then it is atypical.

Therefore, if someone is not a theist, then that person is an atheist.

That's it. Being an atheist says nothing more about a person other than the fact that they are not a theist. It says nothing about their political beliefs, their economic preferences, their age, their gender or their shoe size.

You, too, are an atheist, but you may not even know it. Do you believe in Krishna? Zeus? Odin? Thor? Vatanchu? The list of gods over the centuries numbers in the thousands. It's a safe bet that you don't believe in those either.

Atheists just go one god further.