What does a book mean?

Back in high school, my English teacher liked to give us a form to fill out for each book we read. It listed the obvious bits – author, title, genre – but one of the blanks to fill in was labeled ‘Theme.’ That one always drove me nuts, trying to figure out what the author meant by writing the book. Now that I’m looking at it from the other side, as an author, I can see there’s way more to this subject than just filling in a blank. Ray Bradbury famously stormed out of book readings and interviews