Atheism is, in a broad sense, the rejection of belief in the existence of deities. In a narrower sense, atheism is specifically the position that there are no deities. Most inclusively, atheism is simply the absence of belief that any deities exist. Atheism is contrasted with theism, which in its most general form is the belief that at least one deity exists.

The term atheism originated from the Greek ??e?? (atheos), meaning "without god", used as a pejorative term applied to those thought to reject the gods worshipped by the larger society. With the spread of freethought, skeptical inquiry, and subsequent increase in criticism of religion, application of the term narrowed in scope. The first individuals to identify themselves using the word "atheist" lived in the 18th century.  

On Reaching the Pearly Gates

I don’t believe in the god of Abraham, Isaac, Jacob, Jesus, and Muhammad. But should it turn out that this deity exists and should it ever ask me to explain why I haven't been in a house of worship for decades, here’s what I plan to say:

Oh, I’m sorry. I was under the impression (having read the Prophets) that the truest way to honor a genuinely benevolent god (if one could exist) would be to “do justice, love mercy, and walk humbly” (Micah 6:8). That’s what I’ve tried to do. I had trouble taking seriously the idea that the ticket to paradise was obtained by sitting in a specially designated building one or more more times a week and laying disgustingly fawning praise written by someone else on you. At least that’s not what I’d want from people if I were in your place. Now do with me whatever you think right.