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Question: What does the term “Mush” mean in Mah Jongg?
Answer: “Mush” refers to a house rule that is not officially recognized by the National Mah Jongg League. It involves an optional exchange of tiles after the Charleston phase. Players who choose to participate place tiles they want to exchange in front of their rack, face-down. Each participating player takes back, in turn the same number of tiles they contributed from the other players.
Typically, the standard number of tiles that can be exchanged in the mush is three, although some groups may allow up to five tiles to be exchanged. Another variation of this table rule involves doing a mush after the first Charleston, and if all players agree, continuing with the second Charleston. This ruling is not found in Mah Jongg Made Easy.
See also ID53, The League on House Rules