What is Atheism

Atheism, by definition, is the absence of theism. If you cannot say "I believe in a Deity/God/Supreme Being" then you are an atheist. If you are not a theist, then you are an atheist.
As mentioned in the Introduction page, there is a subtle but important difference between "believing there is no God", and "not believing there is a God". The first is a belief, the second is a lack of that belief. I don't know any atheists who "believe" God (take your pick, there are plenty) does not exist. All the atheists I know simply do not believe God does exist.
There is a big difference between positively believing that a thing does not exist, and simply lacking belief in its existence. In many cases, atheists will say "That God does not exist", not because they choose to do so, but because, from the description of the God, it cannot exist due to contradictory attributes. In the same way that a square circle cannot (and therefore does not) exist, a God defined as (for example) all-knowing, yet cannot see into the future, cannot and does not exist because the definition is self-contradictory. If you describe you’re God with self-contradicting attributes which make it logically impossible, then I may safely say that such a thing does not exist as described. This is not faith - this is reason.
If someone asked you about unicorns, would you say "I believe there are no unicorns", or would it be more honest to say "I do not believe in unicorns"? These are two different answers. Nobody disbelieves in unicorns purely as a matter of personal faith.
Again, apply the same reasoning to the Gods of other religions. Example: if you are a Christian, do you believe the Hindu God Ganesh does not exist? Or do you not believe in Ganesh?
If you believe that unicorns do not exist, then may I say that you a member of the "No unicorns" religion? Is it a matter of faith that unicorns do not exist? Can I come along to your non-unicorn church with you tomorrow?
If you are a Christian, do you believe Ganesh does not exist? Why, then you must be a devout follower of the "No Ganesh" faith!
Do you see where this is going? [Sarcasm may be the lowest form of wit, but it's excellent for getting a point across. 8- )]
If me not believing in your God is a faith, then you not believing in other Gods is an equal faith. How many Christians do you know who would say they do not believe in other Gods as a matter of faith?
If my atheism with respect to your deity is a religion, then your atheism with respect to other deities is also a religion.
Atheism is neither religion nor faith, but the happy freedom from them. Declaring it to be otherwise, sadly, will not make it so.