Machi
Machi 「待ち」 is the Japanese term for "tenpai wait patterns". Given any mahjong hand at any instance, players are waiting for specific tiles either to develop their hands or complete it. Wait patterns arise during hand development, when mahjong tiles in possession in the hand are in need of other tiles in order to complete mentsu (tile groups) or the entire hand. Wait patterns during tenpai are of particular interest, simply because that is one of the main goals of hand development.
Overview
Many different patterns arise during the course of hand development. Once a hand reaches tenpai, being able to interpret the hand's available winning tiles is a vital skill. If a player does not correctly read their winning tiles, they may miss a valid win, or they may commit a chombo with an illegal win call: either by calling a win on a tile that does not complete the hand, or calling ron while furiten due to a tile that they did not realize would complete the hand.
The most commonly occurring wait patterns have been given names, to make them more easily recognizable. More complex waits can arise involving a large number of potential configurations of the hand. This is especially true of hands with a large number of tiles in the same suit, most notably those aiming for chinitsu. Knowing the basic wait patterns also helps to combine them to interpret complex hands, which may have as many as 8 weights (not counting the special cases of chuuren poutou and kokushi musou, which are easily recognizable).
Hand development
During hand development, it is important to understand the hand's machi for two reasons. The first is that, when trying to bring a hand to tenpai, a player will want to maximize the number of available tiles to bring them closer. Doing this requires interpreting the patterns of potential groups in a similar manner to finding tile waits in a tenpai hand. The second is that furiten is best avoided, and so a player should avoid making discards that would leave them furiten once they reach tenpai. This can be a particular challenge when developing single-suited hands that may have a large number of different waits.
Basic wait patterns
These five are essentially the basic wait patterns. Upon tenpai, they only look to complete either the last tile group or the pair.
Ryanmen
Waiting for: 
Penchan
-
Waiting for: 
Shanpon
- Waiting for:
Kanchan
-
Waiting for: 
Tanki
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Waiting for:
Named combinations
Nobetan
-
Waiting for:
Ryanmenten
-
Waiting for: 
Sanmentan
Waiting for:
Entotsu
- Waiting for:
Aryanmen
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Waiting for:
Ryantan
- Waiting for:
Pentan
- Waiting for:
Kantan
- Waiting for:
Kantankan
- Waiting for:
Tatsumaki
- Waiting for:
Chuuren poutou kyuumen machi
Waiting for: Any of the same suit tiles, 1 through 9.
Kokushi musou 13 machi
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Waiting for: Any of the 13 tiles shown here.
Complex patterns
These combinations involve patterns that do not have specific names. Instead, they use combined forms of the other patterns. Furthermore, they mostly consist of consecutive, or closely consecutive, numbered tiles. Recognition of these patterns can produce some significantly powerful waits, which may be immune to suji and have large numbers of waiting tiles.
Related Terminology
Hadaka tanki
'Hadaka tanki refers to when a player has made four tile calls (other than added kans), meaning that they only have one hidden tile left in hand. The hand is necessarily tenpai with a tanki wait. Such a hand is very difficult to defend with, because the player will only have two tiles to choose from.
Jigoku
Jigoku 「地獄」 refers to when there is only one winning tile left to win with. If there is only one wait, this means that the other three copies of the winning tile are all in the player's hand, in a discard pool, in a called group, or visible as dora indicators. If there are multiple waits, this means that all but one of them must be completely used. In English, this is commonly known as the hell wait, a literal translation of the Japanese.
Karaten
Karaten 「カラテン」, or empty tenpai, is the case where there are no tiles left to win with, due to all potential winning tiles already having been used in the player's hand, a discard pool, a called group, or visible as dora indicators. In some rulesets, a hand in this state is considered noten at an exhaustive draw.
Takame and Yasume
'Takame is a potential winning tile which is worth more points than another, called yasume.
External links
- Machi in Japanese Wikipedia
- Forum list of various patterns
- Wait survey quiz in Tenhou.net