I am fond of asking random new people in my life about their beliefs concerning god. I am rather astounded by the number of people who tell me they don't believe in god, but when I ask (or assert) that they then must be atheist, they deny being an atheist. I am not the first to suggest that this is due to a misunderstanding of what it means to be an atheist. So, I shall happily clarify:
Atheism is an absence of belief in the existence of god(s). It is not a religion or a worldview. It is a conclusion based on evidence (or lack of evidence).
Of course, people like to define "god(s)" in their own special way, be it "uncaused cause" or "unmoved mover" or "Omni-whatever entity" or "transcendent creator who interacts with the world and answers prayers" or some other supernatural maker/owner/mover/causer of the universe. To me, god is any kind of supernatural transcendent being.
Lots of people do not believe in a supernatural transcenden being, but they will say things like, "nature is god, and I believe in nature, so I believe in god". If you water down the definition of god to be something entirely naturalistic (god = nature) and don't believe in anything supernatural, then you may as well stop kidding yourself and admit you're an atheist. It's okay. Being an atheist is nothing to be ashamed of, despite what you may have been taught.
Lot's of people like to break atheism down into "strong" and "weak" atheism. Strong atheism is the affirmation of the nonexistance of god(s) - I.E. "god(s) do not exist". Weak atheism is an absence of a positive god-belief, I.E. "I don't believe in god(s)".
One can further clarify one's atheism using the clarifiers "ignostic", "agnostic".
An ignostic is a person who ignores questions of the existence of god until a coherent definition of god is produced. All discussion of god is meaningless until a meaningful definition of god is established. Meaningful, in this case, refers to a definition that is capable of being falsified (I.E. Proven false)
If your definition of god cannot be falsified, then your definition is meaningless. One cannot meaningfully claim that some entity exists if one cannot coherently define it.
Since the word "god" has many different meanings, when someone says "god exists" it is possible for many different prepositions to be asserted. For each individual person's meaning of the word "god", there will be atheists, agnostics, and theists relative to that particular concept of god.
So I am ignostic with regard to your definition of god until you can formulate a coherent definition of it.
I find it especially cute when people say, "I define god as love. therefore, it is easy to prove god, you just have to feel love." They think this is such a simple and undeniable way of proving my position wrong. Alas, it proves nothing, and merely toys with language. Generally, before you begin any discourse/argument/discussion/debate on the existence of god, you need to first define god.
An agnostic is someone who believes that the question of whether or not god exists cannot be known. As such, one can be an agnostic theist or an agnostic atheist.
People who are atheists simply do not believe in a god. This lack of a belief has nothing to do with their morals or where they find meaning in their lives. Most atheists couple their conclusion of atheism with a moral worldview such as secular humanism.