An alphabetically arranged list of headings consisting of the personal names, places, and subjects treated in a written work, with page numbers to refer the reader to the point in the text at which information pertaining to the heading is found. In single-volume works of reference and nonfiction, any indexes appear at the end of the back matter. In a multivolume work, they are found at the end of the last volume. In very large multivolume reference works, the last volume may be devoted entirely to indexes. Works of fiction are rarely indexed. The publisher of a periodical may provide an index to each volume at the end of the last issue of the publication year. For best results, indexing should be done by a professional indexer. Alternate plural: indices. See also: American Society of Indexers.

Also refers to an open-end finding guide to the literature of an academic field or discipline (example: Philosopher's Index), to works of a specific literary form (Biography Index) or published in a specific format (Reader's Guide to Periodical Literature), or to the analyzed contents of a serial publication (New York Times Index). Indexes of this kind are usually issued in monthly or quarterly paperback supplements, cumulated annually. Citations are usually listed by author and subject in separate sections, or in a single alphabetical sequence under a system of authorized headings collectively known as controlled vocabulary, developed over time by the indexing service. Indexing can be either pre-coordinate or post-coordinate. Compare with abstracting service and catalog. See also: author index, classified index, cross-index, geographic index, meta-index, name index, periodical index, subject index, and title index.


From ODLIS, Online Dictionary of Library and Information Science by Joan M. Reitz
http://lu.com/odlis/odlis_c.cfm