Glad you asked.
Surprisingly there's some confusion and misconceptions about the very basic definitions on what it means to be an atheist. So to clear some things up I went to www.thefreedictionary.com.
Here's what they had to say:
atheist (ˈeɪθɪˌɪst)
n 1. (Philosophy) a person who does not believe in God or gods
How's that? Should be simple enough, but thanks to religious dogma, there is often a skewed view of what atheists are. Starting with the idea that an atheist rejects the existence of God. This is false. As close as it may sound, there is a huge difference between not believing something, and believing something is false.
Confusing? Yes. But I'll clear it up.
Matt Dillahunty, host of the internet show "The Atheist Experience" puts it like a jar of marbles. Say you're at a party, and there's a big jar of marbles on the kitchen counter. The host announces that the object of this party game is to correctly guess whether there is an even number of marbles, or an odd, and then the winners will get to split the marbles amongst themselves. Ben and his friends all decide that there must be an even number of marbles. You, on the other hand, disagree with their conclusion.
Ben, having heard this says. "So you think there's an odd number."
"No," you reply. "I just don't think that you can conclude that there's an even number.