The printed matter on book jacket flaps.
Flap copy should motivate the reader to open the book. Usually, the front flap describes the book. The back flap tells the prospective buyer about the author and his or her credentials for writing the book.
Many publishers give special care to this copy since it serves as the “meat” for some book reviewers who may not read a book beyond its flaps when writing a review.
It is also a strong selling feature at the point of sale.