Here's why:

* Latent heat refers to the energy absorbed or released during a phase change (solid to liquid, liquid to gas, etc.) without a change in temperature.

* Fusion is the process of changing from a solid to a liquid.

So, when you add heat to a solid, the energy is initially used to increase the kinetic energy of the molecules, raising the temperature. But once the melting point is reached, the added energy is no longer used to increase temperature but instead breaks the bonds holding the molecules in a rigid structure, allowing the substance to transition into a liquid state.