singleton

1) In object-oriented programming , a singleton class is a class that can have only one object (an instance of the class) at a time. For example, using Visual C++ , the "Application" class is an example of a singleton class. You can only create only one object of an Application class.

2) In set theory (mathematics), a singleton is a set with a single element. An example is the set S of all integer s that are neither positive nor negative. In this case:

S = {0}

3) In certain card games, a singleton is a card that is the only one of a suit in a hand. In the game of bridge, each player is dealt 13 cards and any hand with only one card in a given suit is said to hold a singleton of that suit (which, depending on the play of the cards may turn out to be a strength or a weakness, or make no difference.)