The heat energy which has to be supplied to change the state of a substance is called its latent heat. The latent heat which we supply is used up in overcoming the forces of attraction between the particles of substance during the change of state. Latent heat does not increase the kinetic energy of the particles of the substance, so the temperature of a substance does not rise during the change of state.

Latent heat is of two types: Latent heat of fusion and Latent heat of vaporization.