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The C on the Card, Concealed or Closed and Definition (Article ID 144)
Abstract: We often hear players refer to the letter “c” displayed to the right of a hand on the NMJL card as a “closed” hand. The proper term is a “concealed” hand. Similarly, some players refer to the “x” hands as an “open” hand. The proper term is “exposed”.
When playing a concealed hand, a player cannot call a tile to complete an exposure of three or more identical tiles (i.e., pung, kong, or quint). However, when the hand is ready to win, a player can call a discard to declare mah jongg.
When playing a hand that allows exposures, the player can call a discard at any time even if it not their turn.
Question from a player: Sometimes, I hear players refer to a hand with a “c” to the right of it as a closed hand. Is it okay to say closed, or do I have to say concealed? I noticed on the back of the card it shows, concealed.
Resources: Mah Jongg Made Easy (2020 page 12); Choosing a Hand, back of National Mah Jongg League Card.