What is the triple point ?

Explanation

The phase in which matter exists depends on factors like pressure and temperature.
In some specific situations , matter can coexist in more than one phases in equilibrium.
The graphs of pressure against temperature indicating the phase of matter at different temperatures and pressures is called phase diagram of that substance.

Fusion Curve : A curve AB on a phase diagram such that for values of pressures and temperatures corresponding to the point on it, both solid and liqiuid phases coexist in equilibrium is called a fusion curve.
Sublimation Curve : curve OA is called a sublimation curve becaue for the values of pressures and temperatures corresponding to all the points on this curve, both solid and gas phases coexist in equilibrium.
Vaporization Curve : A curve AC on a phase diagram for all the values of pressure and temperature corresponding to all the points on which liquid and gaseous states of matter coexist in equilibrium is known as the vaporization curve.
Triple Point : The point at which the vaporization curve, the fusion curve and the sublimation curve meet, i.e. the values of particular pressure and particular temperature at which all the three states of matter coexist in equilibrium is called triple point of that substance.
For differnt substances such a state is obtained at differnt specific values of temperature and pressure.
Triple point of water is obtained at the pressure of `4.58` mm Hg and `273.16K` temperature.
Triple point of water is used to fix the scale of thermometers.