No, atheism is the outright rejection of the idea of God. It is a religious belief in itself that requires a faith in the non-existence of any sort of God.
Yes, you are right to point that out; after looking up the definition on wikipedia I saw the nuance regarding "supernatural" and expounded upon that above.
And you also forgot one definition. Namely that of religion:
How so? I generally tend to agree with that definition of religion. Notice how physics overlaps that (cosmology and TOEs specifically).
Please explain what god or gods i believe by not believing in god?
Please explain what atheists believe in?
I already addressed this above. If you have a specific question let me know.