A book does not always end with the story. The last few pages at the back of a novel may contain what is known "as back mater," or, in plain terms, a discussion on some aspect of the book. If you are interested in the different elements of back matter, this podcast will be a helpful resource.
Just as front matter is what you find at the beginning of a book, back matter, simply put, is what you find at the end of a book—the sections that appear after the central story has been completed. These sections of back matter are often supplementary in nature, and often inform the reader about some aspect of the book.