Index (or its plural form indices) may refer to:

Arts, entertainment, and media

Fictional entities

* Index (A Certain Magical Index), Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index'' * The Index, an item on a Halo (megastructure), Halo megastructure in the ''Halo'' series of video games

Periodicals and news portals

* ''Index Magazine'', a publication for art and culture * Index.hr, a Croatian online newspaper * index.hu, a Hungarian-language news and community portal * The Index (Kalamazoo College), ''The Index'' (Kalamazoo College), a student newspaper * ''The Index'', an 1860s European propaganda journal created by Henry Hotze to support the Confederate States of America * ''Truman State University Index'', a student newspaper

Other arts, entertainment and media

* The Index (band) * ''Indexed'', a Web cartoon by Jessica Hagy * ''Index'', album by Ana Mena

Business enterprises and events

* Index (retailer), a former UK catalogue retailer * INDEX, a market research fair in Lucknow, India * Index Corporation, a Japanese video game developer

Finance

* Index fund, a collective investment scheme * Stock market index, a statistical average of prices of selected securities

Places in the United States

* Index, Arkansas, an unincorporated community * Index, Kentucky, an unincorporated community * Index, Missouri, a ghost town * Index, New York, a hamlet in Hartwick and Otsego, New York * Index, Virginia, an unincorporated community * Index, Washington, a town * Index, West Virginia, an unincorporated community

Publishing and library studies

* Bibliographic index, a regularly updated publication that lists articles, books, or other information items * Citation index * The ''Index'', colloquial name for ''Germany's List of Media Harmful to Young People'', published by the Bundesprüfstelle für jugendgefährdende Medien * Index card, used for recording and storing small amounts of data * ''Index Librorum Prohibitorum'', a list of publications which the Catholic Church censored * Index on Censorship, a publishing organization that campaigns for freedom of expression, or its magazine of the same name * Index (publishing), an organized list of information in a publication * Index (typography), a hand- or fist-shaped punctuation mark * Subject indexing, describing the content of a document by keywords * Thumb index, a round cut-out in the pages of a publication * Web indexing, Internet indexing

Science, technology, and mathematics

Computer science

* Index, a key in an associative array * Index (typography), a character in Unicode, its code is 132 * Index, the dataset maintained by search engine indexing * Array index, an integer pointer into an array data structure * BitTorrent index, a list of .torrent files available for searches * Database index, a data structure that improves the speed of data retrieval * Index mapping of raw data for an array * Index register, a processor register used for modifying operand addresses during the run of a program * Indexed color, in computer imagery * Indexed Sequential Access Method (ISAM), used for indexing data for fast retrieval * Lookup table, a data structure used to store precomputed information * Site map, or site index, a list of pages of a web site accessible to crawlers or users * Web indexing, Internet indexing * Webserver directory index, a default or index web page in a directory on a web server, such as index.html

Economics

* Index (economics), a single number calculated from an array of prices and quantities ** Price index, a typical price for some good or service

Mathematics and statistics

* Index, a number or other symbol that specifies an element of an indexed family or set * Index, an element of an index set * Index, the label of a summand in sigma notation, Σ-notation of a summation

Algebra

* Index of a subgroup, the number of a subgroup's left cosets * Index, the degree of an nth root, ''n''th root * Index of a linear map#Index, linear map, the dimension of the map's kernel minus the dimension of its cokernel * Index of a Matrix (mathematics), matrix * Index of a real quadratic form

Analysis

* Index, the winding number of an oriented closed curve on a surface relative to a point on that surface * Diversity index, a measure of distribution or variety in fields such as ecology or information science * Index of a vector field, an integer that helps to describe the behaviour of a vector field around an isolated zero

Number theory

* Index, or the discrete logarithm of a number

Statistics

* Index (statistics), a type of aggregate measure ** Scale (social sciences), a method of reporting data in social sciences, sometimes called an index

Other uses in science and technology

* Dental indices, standardized scoring systems for tooth problems * Indexicality, in linguistics, the phenomenon of a sign pointing to some object in the context in which it occurs * Indexing (motion), in mechanical engineering and machining, movement to a precisely known location * Refractive index, a measurement of how light propagates through a material * Valve Index, a virtual reality headset

Other uses

* ''INDEX'', earlier name for the Reimei satellite * Index:, a Danish nonprofit organization which promotes Design for Life * The Index (Dubai), a skyscraper * Index (crater), a moon crater