Generally, a singleton is something which exists alone in some way. The word is used in several different areas:

• In mathematics, a singleton is a set with exactly one element. See singleton (mathematics).
• In computer programming, a singleton is a common design pattern. It refers to a class which is meant to be not freely instantiated, but have only a defined number of instances. See Singleton pattern. A singleton is also a variable that is only used once in a program, usually indicating a programming mistake. See singleton variable.
• In variable-width encoding schemes for computer character sets, a singleton is a character encoded with one unit, as opposed to characters encoded with multiple-unit sequences.
• In Unicode, a singleton is a character the decomposition of which consists of a single character (e.g. the "ohm sign" (Ω) is decomposed as the "Greek capital letter omega" (Ω)).
• A singleton is a baby that is not a twin or other multiple birth.
• In the wake of the popularity of the novel and movie Bridget Jones's Diary, the word has also become popular as a (self-)description of individuals without romantic partners, particularly applied to 20/30-something females. There is an undertone to this use of ignoring societal pressures towards partnerships.
• In trick-taking games where suit is important, such as contract bridge and Hearts, if a hand contains only one card of a particular suit, that card is called a singleton. Certain bidding systems (notably Acol) add notional value to the hand for a short suit of this type since it exposes the possibility of trumping. Similarly, holding a "singleton Queen" (of Spades) in Hearts is a very disadvantageous position.
• In Whisky singleton describes the last cask or charge of a Whisky.
• In espionage, a singleton is an intelligence officer who works alone, in that he has no supporting network.
• In science-fiction stories involving multiple parallel realities, a singleton is a person, place, or thing that exists in only one reality, regardless of how alike said realities might be otherwise. This is often used as a rationale for travel between those worlds.
• Singleton is the title of a short story by Greg Egan
• In conformal field theory, see singleton field.

Euclid, detail from The School of Athens by Raphael. ... In mathematics, a set can be thought of as any collection of distinct things considered as a whole. ... In predicate logic and technical fields that depend on it, uniqueness quantification, or unique existential quantification, is an attempt to formalise the notion of something being true for exactly one thing, or exactly one thing of a certain type. ... In mathematics, a singleton is a set with exactly one element. ... Computer code (HTML with JavaScript) in a tool that uses colors to help the developer see the function of each piece of code. ... In software engineering, a design pattern is a general repeatable solution to a commonly-occurring problem in software design. ... In object-oriented programming, classes are used to group related variables and functions. ... In software engineering, the singleton design pattern is designed to restrict instantiation of a class to one (or a few) objects. ... In computer science and mathematics, a variable is a symbol denoting a quantity or symbolic representation. ... A singleton variable, in computer programming, is variable that is referred to only once in a piece of code, probably because of a programming mistake. ... A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set (a repertoire of symbols) for representation in a computer. ... Technical note: Due to technical limitations, some web browsers may not display some special characters in this article. ... Fraternal twin boys in the tub Twin births occur in most species. ... Human multiple birth: identical triplet sisters Twins, triplets and other multiple births occur with to varying degrees in most animal species, although the term is most applicable to species in the Placentalia subclass. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Contract bridge, usually known simply as bridge, is a trick-taking card game for four players, usually sitting around a table, who form two partnerships, or sides. The partners on each side sit opposite one another. ... Hearts is a trick-taking game, usually played with a standard deck of 52 cards, in which the object is to avoid taking certain cards in tricks. ... Acol is a bridge bidding system. ... Scotch whisky Whisky (or whiskey) (from Irish uisce beatha and/or Scottish Gaelic uisge baugh, both meaning water of life, and ultimately a calque derived from Latin Aqua Vitae (see below)) is an alcoholic beverage distilled from grain, often including malt, which has then been aged in wooden barrels. ... Scotch whisky Whisky (or whiskey) (from Irish uisce beatha and/or Scottish Gaelic uisge baugh, both meaning water of life, and ultimately a calque derived from Latin Aqua Vitae (see below)) is an alcoholic beverage distilled from grain, often including malt, which has then been aged in wooden barrels. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... See Intelligence Officers ... Greg Egan (born August 20, 1961) is an Australian (Perth-based) computer programmer and science fiction author. ... A conformal field theory is a quantum field theory (or statistical mechanics model) that is invariant under the conformal group. ... It is the field of singletons which are the most fundamental unitary and irreducible representation of the Anti de Sitter group SO(3,2). ...

Places called Singleton

In Australia:

• Singleton, New South Wales
• Singleton, Western Australia, a suburb of Perth, Western Australia

In the United Kingdom: Location of Singleton in New South Wales (red) Singleton is a town and Local Government Area on the banks of the Hunter River in New South Wales, Australia. ... Singleton is a suburb of Perth, Western Australia, located within the City of Rockingham. ... Housing subdivision near Union, Kentucky, a suburb of Cincinnati, Ohio. ... Perth is the state capital and most populous city of Western Australia. ...

• Singleton, Lancashire
• Singleton, West Sussex
• Singleton, Kent a suburb of Ashford, Kent

Ashford is a town in the borough of Ashford in Kent, United Kingdom. ...

People named Singleton

• David Singleton, Musician, temptations page
• John Singleton, American film director
• Valerie Singleton, British TV presenter