triple pointtriple point
a pressure and temperature combination at which the solid, liquid, and vapor phases of a substance exist in contact and in equilibrium with one another: the triple point of water is 273.16°K (0.01°C) at c. 4.6 mm of mercury
The temperature and pressure at which a substance can exist in equilibrium in the liquid, solid, and gaseous states. The triple point of pure water is at 0.01 degrees Celsius and 4.58 millimeters of mercury and is used to calibrate thermometers.
(plural triple points)