A classification of traditional playing card games. Defined on Pagat.com as In these games you must match the rank or suit of the previous card. There may be special cards which are exempt from this rule or have special effects.
In terms of mechanics it is a sub-family of Matching Games and in terms of objective, it is a sub-family of Shedding Games.
Crazy Eights is the original game in the family and is played with a traditional card deck.
The best known commercial member of this family is UNO, but Whot and Speed are older commercial implementations.