What is Indexing?
Indexing is
“. . . an index is a systematic arrangement of entries designed to enable users to locate information in a document. The process of creating an index is called indexing, and a person who does it is called an indexer.” from (American Society for Indexing)
An index is a concise, cohesive, and well-interconnected map to the text. It provides references to the locations of important information and deliberately excludes references to irrelevant information.
There are many types of indexes, including back-of-the-book indexes for nonfiction books, cumulative indexes for journals, and computer database indexes.
The index for a nonfiction book is typically the responsibility of the author. Most authors don't index their own work and few publishers have in-house indexers. 95 percent of indexing is done by freelancers hired by authors or publishers.