A threat refer refers to a move which the opponent must answer directly if he is not to suffer a loss (if the threat is valid!); it may be one of the following:
- A ko-threat, gaining the right to retake a ko.
- A forcing move (kikashi), that the opponent has to answer, but not immediately followed up.
- A sente move played as part of a longer sequence.
A threat may be invalid, meaning that the presumed follow-up does not in fact work; it may be ineffective, meaning that it need not be answered, as there is more profit to be gained elsewhere.
The value of a threat is the amount the player will gain if he gets to play a second move because it goes unanswered. For a forcing move or other sente to be effective, the value generally needs to be higher than the ambient temperature, but for a ko-threat the situation is more complicated, as described at Ko threat - Rule of Thumb.
It is of course possible that a threat is invalid, but is still answered. This happens particularly in the following cases (which often overlap):
- The situation is too difficult for the threatened player to read.
- The threatened player has a very comfortable lead.
- They can, however seldom afford to do this all that often.
- The threatened player is considerably weaker than their opponent.