DustJacket
The dust jacket (sometimes dust wrapper or dust cover) of a book is the detachable outer cover, which is usually printed and often illustrated. This outer cover has folded flaps that hold it to the front and back book covers. Often the jacket provides biographical information about the author and offers a summary of the book from the publisher (known as a blurb), and puffs of critical praise from celebrities or authorities in the book's subject area. In addition to its promotional role, the dust jacket protects the book cover from damage. However, since it itself is relatively fragile, and since dust jackets have intrinsic, aesthetic and financial value, the jacket may in turn be wrapped in acetate or another transparent material, especially if the book is a library volume meant for lending out to patrons.

***Definition taken from Wikipedia