A postface is a fancy word for something that comes at the end of a book, kind of like the end credits of a movie. It's written by the author and explains things like why they wrote the book, how they came up with the story or ideas, what they hope readers will get out of it, and sometimes even a little bit about their personal life. It's a chance for the author to say goodbye to their readers and leave them with some final thoughts or reflections. It's like a little bonus at the end of the book!