Hmm, how best to describe it. The Ajahs are different groups of the White Tower (a group of women who can 'channel'/use magic). I don't know if there's a male rank equivalent in the Black Tower, though.
Ok, a quick rundown for anyone who hasn't read the books (or hasn't been able to get past book one)
There's White, Grey, Red, Brown, Blue, Green and Yellow Ajahs, each with a different focus. Oh, and the Black Ajah, too (for those with a definite evil side!). Browns are interested in knowledge, and often prefer the company of books to people. I think.
So I think there would be a lot of Browns at Chronicles!