People tend to stray from the category of "Atheist" because they think it encloses them too tightly in a box (ironically). But people don´t understand how there are different types of atheists. Usually online descriptions are either too vague or too wordy, so let me summarize the basic few definitions for you in layman's terms:
1. “Weak” Atheists (i.e. "Agnostics"): Neither believes that at least one god exists nor do they believe that gods do not exist; believes that if a God or Gods exists there is no way to know; believes that if a god or gods do indeed exist, it has nothing to do with our lives.
2. “Strong” Atheists: Believe in no gods
3. "Free" Thinkers: Do not allow religious pressures affect whatever beliefs which they conclude to.
4. Secular Humanists: Believe in the power of human potential first and foremost, not God´s.