Someone recently asked, “What is flap copy?”
Flap copy is the blurb that appears on the flap of the dust jacket for a book. It’s written like a “hook,” trying to persuade the reader that they will enjoy reading this book, so go buy it! Sometimes, it’s referred to as jacket copy.
It is the second most important marketing tool for a book, so you probably want to monitor what the publisher writes and suggest revisions as needed. Sometimes, writers also play around writing flap copy as a way to help focus a story. It’s also good to think about marketability before you send the mss off to an editor.
The last Harry Potter book, as published in the US, was remarkable for the absence of any flap copy. They didn’t need to persuade the reader to read the book with teases about the story. Those who would read Harry Potter were going to do it anyway.