Heat absorbed by a unit mass of a solid at its melting point in order to convert the solid into a liquid at the same temperature WordNet 3.0 & Open English WordNet

In thermodynamics, the enthalpy of fusion of a substance, also known as heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure. Wikipedia

Enthalpy Wikidata

The amount of thermal energy which is absorbed by a solid material when melting. OmegaWiki

The amount of heat absorbed by unit mass of a material, at its melting point, that causes a phase transition from solid to liquid. Wiktionary