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

Arts, entertainment, and media

Fictional entities

* Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index'' * The Index, an item on a 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), 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 An index fund (also index tracker) is a mutual fund or exchange-traded fund (ETF) designed to follow certain preset rules so that the fund can a specified basket of underlying investments.Reasonable Investor(s), Boston University Law Review, avai ...

, a collective investment scheme *

Stock market index In finance, a stock index, or stock market index, is an index that measures a stock market, or a subset of the stock market, that helps investors compare current stock price levels with past prices to calculate market performance. Two of th ...

, 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 Σ-notation of a summation

Algebra

* Index of a subgroup, the number of a subgroup's left cosets * Index, the degree of an ''n''th root * Index of a

linear map In mathematics, and more specifically in linear algebra, a linear map (also called a linear mapping, linear transformation, vector space homomorphism, or in some contexts linear function) is a mapping V \to W between two vector spaces that ...

, the dimension of the map's kernel minus the dimension of its cokernel * Index of a

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** '' The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchi ...

* 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 In mathematics, for given real numbers ''a'' and ''b'', the logarithm log''b'' ''a'' is a number ''x'' such that . Analogously, in any group ''G'', powers ''b'k'' can be defined for all integers ''k'', and the discrete logarithm log''b ...

of a number

Statistics

* Index (statistics), a type of aggregate measure **

Scale (social sciences) In the social sciences, scaling is the process of measuring or ordering entities with respect to quantitative attributes or traits. For example, a scaling technique might involve estimating individuals' levels of extraversion, or the perceived qual ...

, 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 In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, ...

, a measurement of how light propagates through a material *

Valve Index The Valve Index is a consumer virtual reality headset created and manufactured by Valve. Announced on April 30, 2019, the headset was released on June 28 of the same year. The Index is a second-generation headset and the first to be manufacture ...

, 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