What does index mean?
An index is an organized guide that helps a reader locate information. Most commonly, it is a list of topics, names, or references arranged alphabetically or numerically, as in a book index. The word also refers to a sign, symbol, or number that indicates a position, value, category, or change over time; economic measures such as a price index are important examples. In a more specialized use, an index is a formal system in which a particular sound or form is associated with a meaning, especially in linguistics. As a verb, “index” means to classify, catalogue, or create an index for information, such as articles, records, or entries in a database. The word is useful because it describes both the physical act of pointing and the broader process of organizing information so that it can be found efficiently.
An alphabetically or numerically arranged list of names, topics, or references that helps users locate information. More broadly, it may be a sign, symbol, numerical measure, or formal system indicating a value, position, category, or relationship.
"The index provides page numbers for every major topic in the book."
The general plural is “indexes”; “indices” is also widely used in mathematics, finance, and some publishing contexts.
To arrange, classify, or catalogue information by creating an index or assigning index entries to it.
"The archive indexes each recording by performer, year, and genre."
This use is common in publishing, information science, libraries, computing, and database administration.
“Indexes” is the standard plural in general use. “Indices” is also accepted, especially in mathematics, finance, and some publishing contexts.
"The library catalog contains several indexes for authors, subjects, and publication dates."
From a Latin word meaning “pointer,” an index has long been a sign that points the way through a vast body of information.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does index come from?
The English word comes through Latin from index, meaning “pointer,” “forecaster,” or “sign,” a noun formed from indicare, “to point out” or “indicate.” The borrowing appeared in English in the late 16th century, initially in contexts involving pointing, signs, and catalogues. Related English words include indicate, indicative, and indication, while indict developed through Old French from a related Latin root.
Related word forms
How index is actually used
The plural “indexes” is the usual general form, although “indices” is also standard in mathematical, financial, and some publishing contexts. In computing, “index” commonly refers to a data structure that enables rapid retrieval. The verb “index” is formal but well established, especially in publishing, information management, and data processing.