Agnostic- does not know whether there are gods or not
one is a question about what you know (or at least believe you know) and the other is a question of what you merely believe. They are not necessarily mutually exclusive. here are some examples from John and and the ever skeptical Mary:
John: I can turn into the Cloverfield monster.
Mary: okay, do it right now so that I may witness your terrible majesty.
John: umm I cant, I can only do it when I'm not being observed.
Mary: Well,I don't believe you. I like you john, but that is a pretty fantastic assertion. (here Mary becomes an atheist...or acloverfieldist)
John: hmm, we are at an impasse
Mary: indeed, wait I have an idea! Lets turn off the lights and then you can turn into the CM. When you grow to enormous proportions you will surely destroy the living room...and you could make some make some giant monster noises to boot. I would accept the mangled ruins of my home and a bone chilling bray as convincing evidence of your claim.
John: Well, not only does my petrifying beast form stymie direct observation, any and all effects,atmospheric perturbations, damages and so forth likewise cannot be observed. When you turn the lights back on everything will instantly revert to its un-obliterated state.
Mary: I must admit that you could turn into the CM when you are not being observed, and I have absolutely no way of proving it one way or another.(agnostic)
John: Right! so now do you believe me?
Mary: absolutely not! you have provided no proof, furthermore there can be no proof. (atheist & agnostic)
Oscar: I'm with Mary, I don't believe it! (athiest)
Mary: Of course you do Oscar, because you are the smartest and most handsome most kind and gentle intell...
Oscar: Please, you make me blush. Anyway I will go a step further than Mary and say that i know that you don't turn into the Cloverleaf monster!
John: Its the Cloverfield monster.
Oscar: What did I say?
Oscar: I'm pretty sure i said Cloverfeild
John: No, and that time you spelled field wrong, its "i" before "e" exce....
Oscar: Whatever, the point is that not only is the monster a fictional beast from an overrated movie, there is no evidence that such a thing could even happen....wait how would you know that I spelled "field" wrong if we're having a conversation?.....Anyway, nothing That we know about the universe even suggests the possibility of such a thing! Therefore I call mishegaas (Still atheist, but not agnostic)
John: its shenanigans!
Mary: I love you Oscar!
Oscar: I know.