There is zero difference between those two words. That's what the prefix "a-" means. Lacking a belief in deities. The appropriate terminology describing anything beyond that exists.

Edit: essentially what I'm saying here is care enough to learn the terminology. Else you risk painting us all with the same brush. Personally, I would never say that the possibility of God is impossible. Strong atheists don't agree with me.

Tomato tomahto you're splitting hairs

I've heard people who just don't care called "apatheists"