n. (indexes, indices, pl.)
An ordered list of headings that points to relevant information in materials that are organized in a different order.
A portion of a book, usually located in the back, that provides an ordered list of subjects covered in the book, with page numbers or other reference to where those subjects are discussed.
A scale or reference used as a measure.
A typographical ornament in the shape of a fist with the index finger extended.
Generally, an index1 provides no explanation about the information it points to beyond its location. It is distinguished from a catalog, which provides additional information to help determine relevance. An index may be created on cards, with separate cards for each entry to allow interfiling. It may also be on paper or in a database or word processing file. - An index2 usually uses page numbers for the pointers, but some works may use section numbers. - Examples of index3 include quality index and time-weighted preservation index.
Dow et al. 2001, p. 295 A superficial examination of a printed index would reveal that search engines available at this writing  could retrieve many of its references from the full text of a work, but it is also clear that they could not build the web of relationships and analysis provided by a good back-of-the-book index, nor the navigational support provided by such an index.