Triple point of water

The graph between the pressure and temperature of a substance describing the boundaries between the phases is called phase diagram. In this diagram the point at which solid, liquid and vapour can co-exist or will be in equilbrium is called triple point. This point represents particular pressure and temperature.
In order to understand this concept, we take the example water for which melting point is at zero degree centigrade and boiling point is at hundred degree centigrade. At melting point, boiling point and sublimation points, depending upon the state of matter, pressure can be rapidly changed but temperature is at constant value. Like this, at certain pressure, water is at solid state and also it reaches sublimation state at temperature zero degree centigrade. At that pressure and temperature,
solid, liquid and gaseous states are co-exist or equilbrium. If it indicates on the phase diagram,
the point at which pressure and temperature which indicates solid, liquid and gaseous states are equilbrium is called triple point. In the above diagram, ice line, steam line and sublimation line indicates line drawing between melting point and pressure, line between boiling point and pressure and line drawing between sublimation point and pressure respectively. Mainly, these lines indicate equilbrium situation between two states. When these three lines are extended, then they intersect at one point is called triple point.