triple point

American  

noun

Physics.

1. the particular temperature and pressure at which the solid, liquid, and gaseous phases of a given substance are all at equilibrium with one another.

---

triple point British  

noun

1. chem the temperature and pressure at which the three phases of a substance are in equilibrium. The triple point of water, 273.16 K at a pressure of 611.2 Pa, is the basis of the definition of the kelvin

---

triple point Scientific  

1. 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°C (273.16K, 32.01°F) and 4.58 mm (611.2Pa) of mercury and is used to calibrate thermometers.

2. Compare critical point

---

triple point Cultural  

1. In physics, the temperature at which all three phases of matter (solid, liquid, and gas) for a given substance can coexist.

---

Discover More

The triple point for water is a little above the freezing point, and is used to define temperature scales.

Etymology

Origin of triple point

First recorded in 1870–75

Example Sentences

See Examples For:

triple point

On larger icy moons such as Titania, another moon of Uranus, the drop in pressure caused by melting would likely crack the ice shell before reaching the triple point for water, the team found.

From Science Daily ● Mar. 2, 2026

At pressures below the triple point, a substance cannot exist in the liquid state, regardless of its temperature.

From Textbooks ● Feb. 14, 2019

Circle each triple point on the phase diagram.

From Textbooks ● Feb. 14, 2019

The triple point of air-free water is defined as 273.16 K. Why is it important that the water be free of air?

From Textbooks ● Feb. 14, 2019

It is possible, too, that long before the triple point is reached the whole liquid will have evaporated.

From Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 7 "Columbus" to "Condottiere" by Various