noun
tenpai with all winning tiles visible on the table
In mahjong, a tenpai hand where every tile that would complete the hand is already visible among discards or melds, making it impossible to win. Also called 空聴牌.
See also: 聴牌
空テンになってしまい、もう上がれない。
I ended up in karaten, so I can't win anymore.
彼は空テンに気づかずにリーチをかけた。
He declared riichi without realizing he was in karaten.
聴牌 (tenpai) is the general term for a hand that is one tile away from winning. 空テン (karaten) is a specific type of tenpai where all winning tiles are already visible, making the hand unwinnable.
From 空 (kara, 'empty') + テン (ten, from 聴牌 'tenpai'). The term describes a tenpai hand that is effectively empty of winning possibilities.