Temperature is a term imported from combinatorial game theory that indicates the urgency of making a play in a game. (For a definition, see Temperature (CGT).) It is typically more urgent to make a play in a hotter game than in a cooler one. Temperature is related to several common Go terms.
While temperature in CGT is a property of a game, go players use the term to describe the whole board, or sometimes a local region of play. Generally, the temperature of the whole board, or simply, the temperature, corresponds to the size of the largest play (its miai value). As the game progresses, the temperature tends to drop. The local temperature corresponds to the size of the largest play in a region of the board. Generally speaking, a gote play lowers the local temperature and a sente play raises it, while if the local temperature stays the same, the play is ambiguous.
The ambient temperature refers to the temperature of the rest of the board besides the local region. In general it is the value of tenuki. As a rule it is time to make a local play when the ambient temperature drops below the local temperature. Sometimes the choice of a local play depends on the ambient temperature. A gote play, which lowers the local temperature, may be played with sente if its gote response is hotter than the ambient temperature. When both a local play by either player and its gote response are hotter than the ambient temperature, the play is double sente.
If two gote plays have the same size (in other words, if they are miai), then their combined temperature is lower than the local temperature of either one. If a play is the last one before a significant drop in the temperature of the whole board, it is tedomari. Tedomari is worth fighting for, as a rule.
Note: It is often useful to think of a game temperature that never rises during the game. Even if a hot battle erupts, as a rule it heats up a local region, while the ambient temperature remains the same.
-- Bill Spight
See also Temperature and Terminology Discussion.