"snap" and "rummy" principle?

[Unregistered]

1. "They involve matching corresponding pairs of cards or pictures, and may be played as a whole-class activity, where everyone must circulate until they find a partner with a corresponding card or picture, or a pairwork or small-group activity, played as a card game on the 'snap' principle."

2. "These may be played as a whole-class activity, where players circulate freely, exchanging articles or cards at random; or as a card game on the 'rummy' principle."

What do they mean by "snap principle" and "rummy principle?

[Tdol]

Snap- a card game where identical cards are matched
Rummy- a card game where tricks are taken by suit and number