what is atheism

[Gilgamesh]

I've know people who share my stance on religion/god to a tee but don't define as atheists, where as I do. There are multiple accepted definitions of atheism. Some say atheism posits that there is no god; others, including myself, say it's the lack of belief in a god. I was made aware by one of the aforementioned people that if strictly speaking semantics, atheism would mean there is no god, since it's a-theism, right? Meh.