The summary on the back of a book is called a “synopsis.” It sums up the plot of a written work, providing a brief description of the main events of the storyline. … Writers use the term “blurb” to describe the text on the back of the book.
Blurb – distinct from the ‘back book cover blurb’ is this 1-2 line endorsement of a book by a celebrity or another author that sits on the book’s front cover. … These are often placed on the back cover of a book along with the back book blurb. They act like testimonials from the text inside the book. The back blurb is a sales pitch to the reader. It’s often called the back or rear dust-jacket of a book.