hidden dora tile (riichi mahjong)
In riichi mahjong, a bonus dora tile revealed under the dora indicator when a player wins after declaring riichi. Only the winning player can use these tiles for additional han.
See also: リーチ
When you win after declaring riichi, you may get hidden dora tiles.
Three hidden dora tiles were revealed at once, turning the hand into a haneman.
Compound of 裏 (ura, 'back, hidden') and ドラ (dora, 'dora tile'), a mahjong term borrowed from English 'dragon'.