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
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| Anjun - Closed | Minjun - Open |
Shuntsu is a meld consisting of three sequential numbered tiles. To form a minjun or open sequence, players are limited to calling tiles from kamicha, or the player from the left. Discarded tiles from the other two players, that are needed to complete this meld cannot be called upon.
Koutsu
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| Ankou - Closed | Minkou - Open |
Koutsu is a meld, consisting of three of the same type of tiles. In English, koutsu are referred as "triplets". Players may develop minkou (open triplets) by calling on discarded tiles, while in possession of pairs.
Kantsu
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| Ankan - Closed | Minkan - Open | Shouminkan - Open (added) |
Kan is a special tile call in the game. This call forms a meld from four identical tiles.