Page proofs are the typeset manuscript showing the layout exactly as it will appear in the finished book, but the pages aren't bound. These days, page proofs are created directly from the author's electronic file, so there's little actual typing involved.
The page proofs show the inside design of the book. For novels, design is a fairly simple matter (compared with text books, which is what I'm used to). My design uses a scarab icon on each chapter opening page, and a futuristic font for the chapter numbers and header (my name on the left - yay! - and the book title on the right). The relevance of the scarab is that my heroine Edie has an implanted scarab shell between her collarbones, and it has great significance for her.
So far, I've gone through the proofs checking that both the copyeditor's and my corrections from the copyedited manuscript were taken in. Next I have to read the whole thing for a final check - my last chance to make any changes (and at this stage, the author pays for changes other than typesetter errors). The publisher hires a proofreader to do the same thing - checking corrections were taken in, and giving the book a final read for other errors. As an editor, I am of course paranoid about any errors slipping through!