I used to call myself an atheist because I didn't "believe in a god", but I have been corrected several times by people since. They have, vehemently in some cases, argued that an "atheist" believes there is no possibility of any type of "god". After reading wikipedia, it seems that the word is used both ways.
Yeah, there is a fringe of 'hard' atheists who believe that anyone who doesn't pretend to have the certainty that they claim has no claim to the term. They're wrong, by the very definition of the term. The term theist is derived from the Greek word theos (god), and by definition it refers to someone who believes in god/gods.
An atheist, by definition, is someone who does not, as the Greek prefix a- means 'without'. So an atheist is someone who is without belief in god. The term indicates a simple lack of belief nothing more and nothing less. If you don't actively believe that god exists, then you're technically an atheist regardless of how much or how little certainty you have in that belief.
A lot of people think that agnosticism and atheism are inherently separate places on the same scale. Basically, that there's a sliding scale re: the certainty of your belief that has theists on one end, atheists on the other, and agnostics in the middle as people who are uncertain. But again, by the definition of the term, agnosticism/gnosticism is fundamentally separate from atheism/theism.
Gnosticism/agnosticism comes from the Greek word gnosis (knowledge), and it describes your position on knowledge/knowability of the existence of god. It's an entirely separate scale from theism/atheism, and as a result you can have gnostic theists (people who are certain that god exists), agnostic theists (people who believe that god exists but are not certain), agnostic atheists (people who do not believe that god exists but are not certain) or gnostic atheists (people who are certain that god does not exist).
FWIW, I consider myself an agnostic atheist: I don't actively believe in god, but I also recognize that there's a ton out in the universe that's both unknown and unknowable to me. As a result, I'm deeply skeptical of anyone who claims to be 100% certain of either the existence or nonexistence of god/gods.