May I be so bold as to attempt a simplistic definition of the difference between an agnostic and atheist?
An atheist says, “I believe there is no god.”
A theist says, “I believe there is a god.”
An agnostic says, “I’m not sure if there is a god. Maybe there is, maybe there isn’t. I don’t know yet.”
The definition Daytripper seems to be suggesting is that of a proactive agnostic, or “seeker”, as I have heard them colloquially named. The alternative is the apathetic agnostic; they don’t know the answer to the meaning of life and they can’t be bothered to find out.
The apathetic agnostic is by far the most common species found in Australia, considering how close it is to our nation creed:
“Australia - We’re interested in apathy.”
Agnosticism is a position on knowledge, while (a)theism is a position on belief. An agnostic says "I don't believe I can truly know for sure", while a gnostic says "I'm absolutely sure", and an atheist says "I don't believe in any gods" while a theist says "I believe in a god or gods". They can be combined in any of the four combinatorial ways you'd expect; there are theists who 'know' there is/are a god/gods, there are atheists who 'know' there are none, there are theists who just think there is/are a god/gods and atheists who just think there aren't.
We also have the "pure" agnostic, characterised by the belief, "I don't know whether or not a god or gods exist, and I believe that it is fundamentally impossible to ever truly know." However, by the definition of "atheist" (one who doesn't believe in a god or gods), these pure agnostics are still atheists.