What is an index? If you’ve ever read a book in your life (which we hope you have) you’ve come across and used an index. The exact definition is, “an alphabetical list of names, subjects, etc., with references to the places where they occur, typically found at the end of a book.” If you crack open almost any non-fiction book, you can find one.
It’s one of those parts of a book that are easily overlooked for how helpful it is until you need it. If you’ve ever had to look up something in a book, you appreciate when an index is properly done.
The last thing you ever want is for your readers to go to your index and not find something that clearly should have been labeled and categorized, or worse, in the wrong place. It’s a small part of the book, but it is constantly used so you want to make sure you’re spending the time to do it right.