Index

An index is an indirect shortcut derived from and pointing into, a greater volume of values, data, information or knowledge. Index may refer to:

Business

• Index (retailer), a defunct UK catalogue retailer formerly owned by the Littlewoods group and known as Littlewoods Index
• Index Corporation, a Japanese video game developer
• INDEX, a market research fair in Lucknow, India
• Index fund, a collective investment scheme
• Stock market index, a statistical average of prices of securities

Publishing

• Bibliographic index, a regularly updated print periodical publication that lists articles, books, and/or other information items, usually within a particular discipline
• Index (publishing), a detailed list, usually arranged alphabetically, of the specific information in a publication
• Index (typography), a (rare today) punctuation mark
• Index cards in a rolodex or old library card catalog, early and mid 20th century technologies for maintaining such lists
• Germany's List of Media Harmful to Young People, colloquially known as The Index, published by the Bundesprüfstelle für jugendgefährdende Medien
• Index Librorum Prohibitorum, a list of publications which the Catholic Church censored
• Index Librorum Prohibitorum, a character from the Japanese light novel, anime and manga A Certain Magical Index. "Index" may refer either to the character, or the series.
• Index Magazine, a New York City-based publication for art and culture
• index.hu, a Hungarian-language news and community portal
• Indexed (cartoon), a Web cartoon by Jessica Hagy
• The Index, the student newspaper of Kalamazoo College
• The Index (journal), a European propaganda journal created by Henry Hotze to support the Confederate States of America during the American Civil War
• Thumb index, a round cut-out in the pages of a publication
• Truman State University Index, the weekly student newspaper

Sciences

• Index (statistics), a concept in statistics, research design and social sciences
  • A scale (social sciences), a more advanced type of an index

Biological sciences

• Diversity index – a quantitative measure that increases when the number of types into which a set of entities has been classified increases, and obtains its maximum value for a given number of types when all types are represented by the same number of entities

Computer science

• Lookup table, a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation
• Array index, an integer pointer (into an array data structure) that identifies an element of the array
• A key in an associative array
• Database index, a data structure that improves the speed of data retrieval operations on a database table
• Index mapping, mapping of raw data, used directly as in array index, for an array
• Index register, a processor register used for modifying operand addresses during the run of a program
• The dataset maintained by search engine indexing
• Indexed color
• Indexed Sequential Access Method (ISAM), a method for indexing data for fast retrieval
• Subject indexing, describing the content of a document by keywords
• Web indexing (Internet indexing)
• Site map, a list of pages of a web site accessible to crawlers or users
• Webserver directory index, a default or index web page in a directory on a web server, such as index.html
• BitTorrent index, a list of .torrent files available for searches

Economics

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

Geography

• Index, New York, a hamlet in the County and Town of Otsego, New York, United States
• Index, Washington, a town in Snohomish County, Washington, United States
• Index, West Virginia

Library and information science

• Back-of-the-book index
• Bibliographic index, a regularly updated print periodical publication that lists articles, books, and/or other information items,
• Index (publishing), a detailed list, usually arranged alphabetically, of the specific information in a publication
• Subject indexing, describing the content of a document by keywords

Linguistics

• Indexicality, the variation of meaning of an utterance according to certain features of the context in which it is uttered

Mathematics

• A number or other symbol that indicates the location of a variable in an indexed family or set such as a list or array of numbers or other mathematical objects, usually written as a subscript to the variable; e.g. in the list $\lbrace x_{1},x_{2},x_{3},x_{4}\rbrace$, the number $3$ is the index of the third element, $x_{3}$.
• A numerical value attached to a mathematical object, such as those listed here under Algebra and Analysis
• The index of summation i is used to calculate a sum, e.g.:

$\sum _{i\mathop {=} 3}^{5}i=3+4+5=12.$

Algebra

• The degree of an nth root
• The index of a subgroup is the number of a subgroup's left cosets (which is equal to the number of its right cosets).
• The index of a linear map, is the dimension of the map's kernel minus the dimension of its cokernel.
• The index of a real quadratic form Q is defined (but not always consistently) as p − q where Q can be written as a difference of p squared linear terms and q squared linear terms.
• The index of a matrix is the least integer k ≥ 0 such that rank(A^k+1) = rank(A^k).

Analysis

• The winding number of an oriented closed curve on a surface relative to a point on that surface; loosely speaking, the number of times the curve goes around the point counter-clockwise
• The index of a vector field v at an isolated zero is the degree of the map $x^{a}\mapsto {\frac {v^{a}(x)}{\sqrt {\sum _{b}(v^{b}(x))^{2}}}}$, taking points near the zero into the unit sphere.

Technologies

Mechanics

• Indexing (motion), a kind of motion in many areas of mechanical engineering and machining

Optics

• Refractive index, a measure for optical properties of transparent materials.

Other usages

• Index finger, the second digit of a human hand
• Index:, a Danish nonprofit organization which promotes Design for Life
• Index Ventures, a venture capital investment firm based in Switzerland
• The Index, an item on a halo megastructure in the Halo series of video games
• The Index (Dubai), a skyscraper in Dubai
• FamilySearch Indexing including indexing the US 1940 Census
• Congregation of the Index, former dicastery of the Roman Catholic Church