surplus tile; unnecessary tile at tenpai
In mahjong, a tile that is no longer needed to complete the hand, especially the tile discarded when reaching tenpai (ready hand).
See also: テンパイ
When you reach tenpai, you discard the surplus tile and declare your wait.
どの牌が余剰牌かを見極めるのが難しい。
It's difficult to determine which tile is the surplus one.
Compound of 余剰 (surplus) and 牌 (tile), a straightforward mahjong term.