For aviation purposes, 59°F (15°C).
zero degrees Celsius.
exactly zero degrees Centigrade
Adopted by International Civil Aviation Organization: mean sea level (MSL), pressure 1013.25 mb, temperature 15 degrees C.
Sixty degrees Fahrenheit, based on the international temperature scale.
The temperature at which the parameters of a given ionic model have been specified.
In physics, usually the ice point (0°C); less frequently, the temperature of maximum water density (4°C). In meteorology, this has no generally accepted meaning, except that it may refer to the temperature at zero pressure altitude in the standard atmosphere (15°C).