What role does an appendix typically play in a book?

The role of an appendix in a book is to provide necessary supplementary information that supports the main text without interrupting its flow. This supplementary information can include additional details, data, explanations, or resources that enhance the reader's understanding of the content but are not essential to the core narrative or arguments presented in the main chapters. The appendix allows the author to include this information in a structured way, making it easier for readers to refer to it as needed while maintaining the focus on the primary material of the book.