Books at the moment for me are still paper-based collections of words. Most are novels or stories, I don’t honestly read a lot of really good non-fiction work I must admit. I also have yet to have a good enough portable system to read ebooks, although I still have a fair amount of normal books to read through in any case.
While also book-like, I’m putting graphic novels and comics under the Comics page. Books are generally text only, perhaps with the odd illustration or embellishment, and each works in very different ways.