Game-deciding Ko
A ko which is so large that any ko threat on the board can be ignored, since winning the ko means winning the game. The Japanese, tenka-kikazu (or tenka-ko), means literally "there is no threat under the sun".
From Nihon Ki-in, Shin Hayawakari Yougo Kojiten: "Tenka-ko: a ko so large as to determine the outcome of the game (shoubu ga kimatte shimau). A ko that, no matter where the other side plays a ko threat, if resolved yields victory (kachi ni naru)."