Mentsu
Mentsu (面子) are the melds used for the game. The melds follow a similar pattern to the regular card game, gin rummy. The melds are subdivided into three types: shuntsu (sequence), koutsu (three-of-a-kind), and kantsu (four-of-a-kind). Forming these melds is a central part of developing a mahjong hand to the point of tenpai and even winning the hand. Two factors go towards the formation of melds: suit and number (or type).
The melds
While the melds are subdivided into three types, they are further subdivided into the state of open or closed.
Shuntsu
Shuntsu is a meld consisting of three sequential numbered tiles.
Koutsu
Kantsu
Main article: Kan
Kan is a special tile call in the game. This call forms a meld from four identical tiles.