tie-in

a fastener that serves to join or connect

a type of book that is based on a media franchise, such as a movie, TV show, or video game, and is often released to coincide with the release of the franchise

A tie-in is a product, often a book or media item, that is related to or promotes another work, such as a movie, TV show, or event. Tie-ins are created to benefit from the popularity of the original work, offering additional content or expanding on its themes. For example, a movie tie-in book might provide behind-the-scenes details, story expansions, or adaptations of the film’s script. Tie-ins aim to enhance the audience's experience and connect with fans of the original work.