This article is from the Atheism FAQ, by mathew firstname.lastname@example.org with numerous contributions by others.
Atheism is characterized by a deliberate absence of belief in the
existence of gods. Some atheists go further, and believe that
particular gods do not exist. The former is often referred to as the
"weak atheist" position, and the latter as "strong atheism".
It is important to note the difference between these two positions.
"Weak atheism" is simple scepticism; disbelief in the existence of
God. "Strong atheism" is a positive belief that God does not exist.
Please do not fall into the trap of assuming that all atheists are
"strong atheists". There is a qualitative difference in the "strong"
and "weak" positions; it's not just a matter of degree.
Some atheists believe in the non-existence of all Gods; others limit
their atheism to specific Gods, such as the Christian God, rather than
making flat-out denials.
"But isn't disbelieving in God the same thing as believing he doesn't
Definitely not. Disbelief in a proposition means that one does not
believe it to be true. Not believing that something is true is not
equivalent to believing that it is false; one may simply have no idea
whether it is true or not. Which brings us to agnosticism.