According to the American Atheists website they state this
Atheism is one thing: A lack of belief in gods.
Atheism is not an affirmative belief that there is no god nor does it answer any other question about what a person believes. It is simply a rejection of the assertion that there are gods. Atheism is too often defined incorrectly as a belief system. To be clear: Atheism is not a disbelief in gods or a denial of gods; it is a lack of belief in gods.
What is Atheism? | American Atheists
But in many discussions in this forum with many good Atheists i come across many ways to describe what atheism is.
Could i get some more info from Atheists in this forum? What is Atheism to you?