concealed kong; declaring a concealed kong
In mahjong, the act of forming a kong (four identical tiles) entirely from tiles in one's hand, without having called any of them from discards. The set is kept concealed until declared.
from Chinese àngàng
See also: 槓
When declaring a concealed kong, you place the four tiles face down in a row.
He had four identical tiles in his hand, so he made a concealed kong.