índex

An index is a systematic list or catalog that points readers to the location of information within a document, a collection, or a broader domain. The word derives from the Latin indicem, meaning a sign or pointer. In general use, an index helps users locate topics, names, or data quickly, often by pairing entries with page numbers, sections, or data references.

In publishing and libraries, an index is typically a structured list of keywords or topics found in a work, sometimes including proper names, places, and important concepts. A book index allows readers to find where topics appear across chapters and pages. In scholarly and technical works, indexes are designed to enhance navigability and thematic finding.

In computing and information retrieval, indexing constructs data structures that enable fast search. An inverted index, for instance, maps terms to their occurrences in documents, speeding up query processing in search engines and databases. Database indexes, such as B-trees, optimize data retrieval by providing quick access paths to records.

In finance, a stock market index aggregates the performance of a selected group of assets to act as a benchmark for overall market movements, with examples like the S&P 500 or the Dow Jones Industrial Average. In mathematics, an index (or subscript) denotes the position of an element within a sequence, and index notation is used in summations and formulas. In semiotics, an index is a sign that suggests a causal or physical connection to its object, such as smoke indicating fire.

The term appears in several languages with similar meanings, including í index variants in various Iberian and Romance languages. A historical example is the Index Librorum Prohibitorum, a list of prohibited books issued by the Catholic Church.