I was never raised religious. My family was "officially" some kind of non-specific Christian though we never attended church and my mother subscribed more to a vague new-age type of spirituality. When I asked "why" questions, I was mostly given the actual, scientific answer.
So I have always held largely the same beliefs. When I was young I was very interested in stories of the supernatural and strange mysteries and perhaps even wished for such things to be real, but I've become much more skeptical the more I learn.
I would probably have been fine being called a "pantheist" or a "deist" or an "agnostic." I believed in keeping my mind open and besides, some people choose to use the word God synonymously with Nature, or simply to imply that Nature is fundamentally understandable by humans (something I believe, which could be called a matter of faith). This is basically the way Einstein would use the word "God." God seems such a nebulous and constantly changing concept to many people that there is no point in denying the existence of such a thing/being/whatever.
However, the social and political state of things in the United States has changed my mind, or at least the words I use. I didn't draw the lines in the sand, the religious right did. When I kept seeing Einstein's quotes used by biblical literalists and religious fundamentalists to support their assertions, I realized the need to be more clear. You are either with or against the fundamentalists and they will claim all the fence-sitters as being in their camp to boost their numbers and credibility.
So I am an atheist. I do not believe in the God described in the Old Testament, or the one in the New Testament or any of the other major religious books. I do not believe in Zeus, or Odin, or any of these gods either. I do not believe in supernatural deities with human-like thoughts who meddle in the workings of the Universe. This is what the fundamentalists are talking about when they say "God" so this is the definition I will have to use as well, lest I be misunderstood and misrepresented.
This is why I call myself an atheist.