Suppose that Black begins a ko by taking a stone of White's. White cannot immediately recapture; the rules state that he must, for the moment, play elsewhere. White may believe that good strategy requires he/she eventually recapture, but Black, on his/her next turn, will have the option of ending the ko, for example by filling in the spot White would use to recapture. To prevent Black from doing this, White can play a ko threat.

A ko threat is a move that forces one's opponent to respond, or risk a punishing blow. A ko threat by White will force Black to choose between responding to the threat, and allowing White to recapture (thereby continuing the ko), or ending the ko, but having a damaged, poor position elsewhere on the board.

A good ko threat should threaten more damage to one's opponent position than the value of losing the ko. If then the ko is lost, the trade was still beneficial.