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. Incidentally, some players refer to the “x” hands as “open” hand . The property term for this type of hand is “exposed”. It is acceptable to use closed for concealed and open for exposed with no penalty incurred.
The letter “C” to a hand’s right indicates one cannot call to expose tiles during the game.