If a player has three similar tiles in hand and he receives a fourth similar tile from the Wall, he can declare a concealed Kong. The tiles composing a Kong may also be kept in hand to declare a Kong at a later time. When the set is declared as a Kong, the tiles composing the set are normally turned face up and placed above the hand tiles. After that the first and fourth tile in the set are turned face down, marking the set as concealed (see picture below).
Concealed Kong is normally melded by turning the 1st and 4th tile face down.
If you want the concealed Kongs to be melded face down, check the Hide concealed Kongs box on the General option page under the Rules section in the category tree of the Preferences dialog box.
In some rules concealed Kongs are melded all tiles of the set face down.
Since a Kong consist of four tiles, and you must have four complete sets plus a pair in order to go out, you receive a supplement tile from the Dead Wall.
Note: A Kong must always be declared: if you have four similar tiles in hand
when the deal ends, youll receive points only for a Pung (in case losers are paid for Pungs).
Notice too that some rules restrict player's right to declare a Kong to his own turn, i.e. the player is not allowed to declare Kong after having claimed a discarded tile, but only after having drawn a tile from the Wall. For details, see Kong options.
Declaring a Kong
Goal of the game
Regular pace of the game
Declaring a melded Kong
Robbing a Kong
Deal ends in a Draw
Faulty declaration of Out