Seth Godin's "short head" vs. "long tail"?

I just finished Seth Godin’s This Is Marketing, and I’m a little confused on the difference between “short head” and “long tail.” Not sure if anyone else is familiar with the book, but is it correct that, applied specifically to books, “short head” would refer to the authors who have one or two bestselling books and are successful that way, while “long tail” refers to the authors who are super productive and publish dozens of books and can make a living even though no one book sells a huge number of copies?