Concealed tiles (hidden or standing tiles) are tiles that are in your hand. If you have a concealed chow or pung you have no obligation to announce it or reveal it. Heck, you have no obligation to even use it for your winning hand.
If you have a concealed kong, on the other hand, and if you want to use it as a set you have to announce it on a turn where you drew a tile (i.e. not when you claimed a discard). Concealed kongs are placed face down and set aside next to your other melds. In this case it acts very similar to a melded set: the tiles cannot be placed back into your hand, separated, or re-arranged with any other set.
These hands must be fully concealed and all tiles must be self-drawn with the exception of the last tile.
- Nine Gates
- A hand consisting of 1112345678999 of one suit. It can go out on any other tile from that suit.