Singleton

In poker, a singleton is a card whose rank does not match that of any other in a hand.

For example, if a player has 5♠ and K♢ as his hole cards and 5♣, 7♣, 5♢, 7♢, and 2♠ come up during the flop, fourth street, and river, then the king and the 2 are singletons.

Singleton:

•  a card whose rank does not match that of any other in a hand.