A paperback insert is a promotional or informational material that is included inside a paperback book. It can take the form of a bookmark, postcard, or flyer and is often used to advertise other books by the same author or publisher, provide additional content related to the book, or offer exclusive discounts or promotions. These inserts are designed to enhance the reading experience and engage readers with the book and its related content. They are commonly found in mass-market paperbacks and serve as a creative and effective marketing tool for publishers and authors.