This is a printed paper wrapper to cover a hardback book. Each end folds inside the book itself to protect the cover, which in the older days might have been made of fine leather and linen cloth with a simple embossed title on the front and spine. Today, a dust jacket might be more important than the embossed cover, as it is designed to be eye-catching and to project a meaningful message about the contents.
Many books are created as paperback, meaning the front cover takes the place of the dust jacket as a sales piece to communicate information about the book. It is designed with help sometimes from an illustrator or photographer and is usually printed in full color. Many on-demand resources are available for the self-publisher.
This is the area where the pages are bound. It's often the only part of the book that is visible in the bookstore. The spine usually contains the book’s title ( maybe the subtitle), the last name of the author, and the publisher’s logo.
Further information about the book and author is found on the flip side of the book, on either the dust jacket or the back paperback cover. Included elements are often the author bio and photo, description of the book, advance critical acclaim for the book or endorsements of the book, and the author's other published titles.