Number cards are distinguished by the lack of symbols or illustration added to the cards. These types of cards have usually a single number printed on the card and are largely used in the commercial card game industry.
Popular games that use this type of card format are Uno and Rook, and because of Rook’s popularity, it has spun off into its own modification of the traditional number card deck.
The rook deck was first established in the early 20th century, and while originally intended just for the original deck quickly became its own creation. Several types of rook decks sprouted from this original format and now it’s the most popular type of number card deck to date.