pair

A pair is a unit consisting of two elements treated as a single entity. The elements may be related in use, function, or appearance, and the term is commonly applied to two objects that are kept together or considered together.

In mathematics, a pair often means an ordered pair (a, b), where order matters. An unordered pair is a two-element collection where order is irrelevant, often denoted {a, b}. Pairs underpin coordinates, functions, and basic constructions.

In computer science, a pair is a simple data structure that stores two values, possibly of different types. It is used for associations such as key–value pairs or to return two results from a function.

In everyday language, pair describes two items used together, such as a pair of shoes or a pair of gloves. The phrase appears in many idioms and expressions.

In biology and social science, a pair can refer to two individuals linked by a bond, such as a mating pair or a long-term social pair.

Other uses include pairing in games or analysis, and mathematical pairing functions that map two natural numbers to one, or the way two elements are matched in a combinatorial setting.