What does it mean to say there is no God?

Here is a great quote from Cynthia, "Reverend Mom":

But for me, saying "there is no God" is like saying "there is no mystery" or "there is no transcendence".... And as Marcus Borg has been known to say as well, the God that most atheists denounce, I don't believe in either. Jillette names the God of religious belief as omniscient, omnipresent and omnipotent but as most folks who don't believe in God or believe there isn't one, he doesn't go any further to try to conceive of a God who isn't any of those things--because if God isn't any of that, then it is argued, God isn't God. Just who gets to decide what or who God is? It's all of us, not just church fathers or seminary professors or theologians. Does that mean the mystery disappears? Of course not. How could the mystery of being and breathing and living and dying just disappear because someone believes there is no God? That's just one way of defining the mystery amongst countless others. And when you think about it, it's not very original.