What is the definition of the latent heat of fusion?

The heat energy required to convert either solid to liquid or vice versa is called is called latent heat of fusion.

Consider example of an ice cube. At -10°c, -5°c and at -2°c it is solid. As the temperature goes to 0°c it changes into liquid.If temperature is further increased there is no change and ice remains in its liquid form. The heat required to change solid ice into liquid at 0°c without change in temperature is called latent heat of fusion