Index, in literature, expresses that part of a work, or single volume, which is generally subjoined to its conclusion, and arranged in alphabetical order, with particular references to the pages where the respective matters or subjects are discussed.

An Index should be distinguished from what is usually called, Table of Contents, which affords an analytical view of the different topics, progressively, while the index is intended to facilitate occasional reference. Both are useful: the former, to enable the reader to take a comprehensive survey of the whole work, and to appreciate at once the author's logical talents of dividing and arranging the subject of which he treats, as well as to form an idea of its extent and importance. In an economical respect, however, the latter is a more valuable addition to a book than an analysis of its contents, which are in a manner evident from the heads of chapters or sections; whereas an index tends to save time and labour, that are often unnecessarily wasted in searching for particular passages. Hence a large, ponderous volume, without an alphabetical index, may be aptly compared with an extensive street, or town, the houses of which are not provided with numbers.