(physics) The ratio of the speed of light in air or vacuum to that in another medium.

(information science) An indexing algorithm which indexes a document based on the keywords being searched for.

A piece of heavy paper stock used to record information to be stored in an index.

(information science) A term that captures the essence of the topic of a document, used as keyword to retrieve documents in an information system, for instance a catalog or a search engine.

(economics) A measure of the size of firms in relation to the industries they operate in, serving to indicate the amount of competition among them.

An author-level metric that attempts to measure both the productivity and the citation impact of the publications of a scientist or scholar, based on a set of most cited papers and the number of citations in other publications.

A measure of the reward that can be achieved through a given stochastic process with certain properties.

plural of index digit

(zootomy) In other animals that digit corresponding to the human index finger.

(statistics) A statistic for gauging the similarity and diversity of sample sets, based on the size of the intersection between the sets divided by the size of the union of the sets.