An index is a finding tool that allows a searcher to look up a topic and quickly learn where information on that topic is located within a specific work.

For example, many print books have an index, usually at the back. The index is an alphabetical list of the topics in the book. Under each topic, page numbers are given that show where information on that topic can be located.

Sometimes an index can stand by itself. For example, the Cumulative Index to Nursing and Allied Health (CINAHL) is available as both a print and electronic index. The print index lists articles from hundreds of journals, all arranged under an alphabetical list of topics. You can look up a topic such as Heart Surgery and get a list of citations to articles on that topic. You can do a similar search in an electronic version of CINAHL and get a similar list of citations by doing a subject or keyword search.