Latent heat of vapourisation is a physical property of a substance. It can be defined as: "When a material in liquid state is given energy, it changes its phase from liquid to vapour without change in temperature, the energy absorbed in the process is called latent heat of vaporization".
For example, when a pot of water is kept boiling, the temperature remains at 100 °C (212 °F) until all water evaporates, because here all the heat which is being added to the liquid is absorbed as latent heat of vaporization.