what is it to be agnostic?

A believer believes in God.

An atheist does not believe in God at all.

An agnostic is in the middle - they are not sure one way or the other.

Agnosticism refers to a philosophical stance where one regards the existence of God as unknown or unknowable. It's not a religion as such, so agnosticism covers a range of beliefs. In fact, it's possible to be an agnostic Catholic, for example (i.e. one practices as a Catholic but holds that intellectually one cannot conclusively demonstrate the existence of God by logic). It goes all the way to those who regard supernatural existence as empirically unknowable and even "apathetic agnostics" who simply don't care about the existence of God.

It means you believe there is a possibility of something out there bigger than us, but you don't believe that it's "God"

You believe there is no proof there is a god/deity, but there is also no proof that there isn't a god/deity.

http://en.wikipedia.org/wiki/Agnosticism

basically, you believe that it is impossible to know 100% whether or not a god exists.

to be agnostic means to belive there is a god,but you don't belive he is there

It means you question what has already been fully answered in the Bible.