Cross-reference is a method used in books, indexes, library catalogs, and filing systems to direct attention to additional information about a subject in another part of the book or index. Cross-references are widely used in encyclopedias, dictionaries, and textbooks. For instance, this article on Cross-reference mentions indexes. At the end of the article there is a cross-reference reading "See also Index. " The reader can find more information about indexes in that article. This type of cross-reference is sometimes called a related subject or a related article.