Origin of Triple point of water

Before discussing about this topic, we should know that the matter undergoes three different states
known as phases. During the change of state, there is loss of heat or gain of heat. At constant temperature only, change in state occurs. At a definite pressure and temperature three phases occur. This property is applicable to all substances.
At constant temperature, a solid changes its state as liquid, then it is known as 'melting'. At constant temperature, a liquid changes its state as gas, then it is known as 'boiling'.
It is important point to remember that the heat supplied to the substance which causes to increase the inter-molecular distances.
Above diagram shows that how the water can undergo three different phases at definite temperatures.