Indeed, tonight I will complain about the meaning of agnosticism, as I had said I might do yesterday. Because I find this issue highly annoying!

Agnosticism is not a third category somewhere in between theism and atheism. You either believe in the existence of a god, or you don't. You are either a theist or an atheist. If you don't know whether there is a god or not, you clearly do not believe in one, and are therefore an atheist. Guh.

There are two kinds of agnostics. Those that are theists, and those that are atheists. Agnostics have doubts, of various degrees, about what information can be known about god/ultimate reality/etc. Agnostic theists believe that it is impossible to know the nature of god, but do believe that it is possible to know that one exists. Agnostic atheists believe that even less can be known, to the point where they belive it is impossible even to be sure of a god's existence. Agnostic atheists are not always labelled as atheists. Often they are just plain called aganostics, as though it were a third category. And only non-agnostic atheists, who believe that it IS possible to know the nature of god (i.e. that there isn't one), are labelled as atheists. This is wrong. Wrong, I says! So-called "agnostics," who aren't sure whether or not there is a god, and who therefore do not believe in a god, are atheists.

To summarize:
Agnostic theist - Believes in a god. Does not believe that this god's nature is knowable.
Non-agnostic theist - Believes in a god. Believes that this god's nature is knowable.
Agnostic atheist - Does not believe in a god. Does not believe that a god does not exist. (Weak atheist - this is not a belief.)
Non-agnostic atheist - Does not believe in a god. Believes that a god does not exist. (Strong atheist - this is a belief.)

Rant concludes.