Wow, that's an interesting definition of atheism, dk.
I've always known atheism as a lack of belief in G*D -- the opposite of theism, as that definition says.
To assert that it's unknown if there's a G*D or not, I've always known to be agnostic. It cannot be proved that there is a G*D, nor that there is no G*D. Therefore, anyone who follows this belief is an agnostic, NOT atheist.
Your definition combines the two into one. I don't agree with that idea, but, so what? lol!
Where'd you get this definition?
Just curious.
Shalom!