What is Midlist?

The ever thoughtful Jim C. Hines has another excellent post over on his livejournal. Today, he's wondering what does it mean to be mid-list?

I think most of us think of ourselves as mid-list, even though it's a term that's very nebulous and has never been defined for me by any professional, like my editor. We writers tend to talk to ourselves about such things, and make a lot of educated guesses. I think as long as I'm not, as Jim echoes, not J.K. Rowling, Stephen King or other obvious multi-millionaire type writers, I'll probably think of myself as mid-list, right or wrong.