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. Particularly at tenpai, the specific patterns themselves take on names. Tenpai is a critical state of the hand; as after all, this is the point where the hand seeks to win. Therefore, they are of particular interest during tenpai. Some patterns are so complex, such that it helps knowing the wait patterns, especially when different types may work in conjunction. By knowing the different wait patterns, players may be able to determine waiting tiles quickly and more efficiently. This is especially true when dealing with chinitsu and even honitsu hands, where determining waiting tiles may become more complicated and intertwined.
Mentsu
Mentsu are the tile groupings used to develop and compose the hand. To form a complete hand, players must possess 4 melds and a pair. Though, there are three exceptions to the pattern, namely: chiitoitsu, kokushi musou, and nagashi mangan.
Hand development
Basic wait patterns
Ryanmen
Waiting for: 
Penchan
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Waiting for: 
Shanpon
- Waiting for:
Kanchan
-
Waiting for: 
Tanki
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Waiting for:
Nobetan
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Waiting for:
Named combinations
Ryanmenten
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Waiting for: 
Sanmentan
Waiting for:
Entotsu
- Waiting for:
Chuuren poutou kyuumen machi
Waiting for: Any of the same suit tiles, 1 through 9.
Junsei 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.
Special
Jigoku 「地獄」 is a special pattern, which can utilize any wait pattern listed here or among the complex patterns. Although, this condition is more likely to occur among the simple patterns, especially that of the single tile waits of penchan, kanchan, and tanki. The only criteria for jigoku is the number of tiles available to win, and that number is one. This is made possible by the unavailability of another copy by virtue of the discards, one's own hand, or dora indicators.
External links
- Machi in Japanese Wikipedia
- Forum list of various patterns
- Wait survey quiz in Tenhou.net