I believe what you are referring to is actually called agnostic. Agnostic means you believe in the existence of something, but you don't know what it is or you believe that humans cannot fully know what it is. Atheists don't believe in a deity of any sort or definition. A- means without and theism is referring to the believe in a god or gods.
As for bettism, I'd say definitely a philosophy. To live one's life to the fullest, love everyday, wiggle around for treats, and don't take crap from anyone...even yourself in a mirror ;)
Jelly and Pina