An index is a searchable list of keywords, each of which corresponds to one or more topics. The author of a well-designed index anticipates which words and phrases the reader is likely to look for and associates them with matching Help topics. In an online Help system, selecting a keyword displays a list of the associated topics (or the topic itself if there is only one). In a printed manual, the index at the back of the book shows the page numbers that correspond to each keyword.
The following figure shows the Index tab in HTML Help.