nagashi mangan; win by discarding only terminals and honors in a drawn round
A special mahjong hand awarded when a player discards only terminal tiles (1s and 9s) and honor tiles (winds and dragons) throughout the hand, and the round ends in a draw. The hand is worth a mangan (満貫) score.
Nagashi mangan is achieved when all of one's discards are terminals and honors and the round ends in a draw.
From 流し (nagashi, 'flowing' or 'discarding') + 満貫 (mangan, a mahjong score limit). The name describes discarding only terminal and honor tiles throughout the hand to achieve a mangan score.