What atheism is to atheists is often assumed by theists. There seems to be a misconception that it is as big a part of an atheist's life as religion is of a theist's life, as if to say atheism defines the atheist. I'm not here to tell you what atheism means to every atheist; I'm here to tell you what it doesn't mean and what it means to me. This is my atheism.
Atheism isn't a collective belief; it is a collective disbelief. This is an important distinction, for there is no doctrine to follow and nothing to worship. Atheism has no specific statements about the world other than not believing in god claims; it makes no claims itself. Atheism isn't a worldview; it is the rejection of theistic worldviews. Atheists can hold a variety of worldviews, but their atheism only means they don't accept those based on gods—at least not without evidence.
Saying atheism is a worldview by which to live is like saying non-American is a nationality. And I don't define myself as a non-American; I am Swedish. Saying atheism is a worldview like religion is like saying not being a capitalist is a worldview like capitalism. I do not define myself as a non-capitalist; I am a social democrat. I have an alternative nationality to American and an alternative ideology to capitalism, but I do not have an alternative to being a Christian or a Muslim. This is why, in this instance, it is meaningful to use the negative term, such as non-believer or atheist, even though atheism isn't an ideology in and of itself.
Many atheists wear their atheism on their sleeves. They do this, not because of atheism, per se, but because of the oppression, bigotry, and ignorance that comes from religion, even though not all theists are bad people (in fact, most theists are probably good people). Atheists call themselves as such because they oppose or don't accept religion, not because they define themselves as atheists, per se.
My atheism is only a part of me because religion cannot go on unhindered. My atheism is simply my non-acceptance of crazy and baseless god claims. My atheism has nothing to do with how I live, except that I don't follow religious doctrine. My atheism doesn't make me a better person, but it also doesn't make me a worse one. My atheism is not dependent on current scientific theories, but lets me embrace science as a field of logic and evidence. My atheism is my non-religion.
Atheism doesn't mean atheists have anything in common except for their disbelief in gods. What atheism means for a person's life varies. Tell the world what your atheism means to you with the hashtag #MyAtheism.