copula

1. (linguistics, grammar) A word, usually a verb, used to link the subject of a sentence with a predicate (usually a subject complement or an adverbial), that unites or associates the subject with the predicate.Examples: "I begin by arguing in section 2 that there are in fact at least two Celtic copulas, a grammatical copula that simply spells out tense and agreement, and a substantive copula formed on a lexically listed verbal stem."; "The theory of conjunctively tensed copulae will be developed and stated with more precision in the following section."; "This paper explores the position of the copula in the development of the verb system in second language acquisition of Italian."

2. (statistics) A function that represents the association between two or more variables, independent of the individual marginal distributions of the variables.Examples: "In 2000, David X. Li, a banker with a doctorate in statistics who was then at RiskMetrics, part of J. P. Morgan Chase, began using mathematical functions called Gaussian copulas to estimate the likelihood of corporations’ dying in unison."; "There is little statistical theoretical theory for copulas. Sensitivity studies of estimation procedures and goodness-of-fit tests for copulas are unknown."; "Copulas provide an example of the haphazard evolution of quantitative finance. The key result is Sklar's theorem, which says that one can characterize any multivariate probability distribution by its copula (which specifies the correlation structure) and its marginal distributions (the conditional one dimensional distributions). Thus one can create multivariate distributions by mixing and matching copulas and marginal distributions."

3. (music) A device that connects two or more keyboards of an organ.

4. (biology) The act of copulation; mating.