A book index is a systematic list of topics, terms, or names found in a book, usually located at the end. It helps readers quickly locate specific information by providing page numbers where each entry can be found. This feature is especially useful in non-fiction books, such as textbooks or reference books, where readers may need to find particular facts or concepts. Indexes are typically organized in alphabetical order, making it easy to navigate. They may also include sub-entries for more detailed topics, allowing for a more comprehensive search. A well-constructed index enhances the usability of a book, improving the overall reading experience.