Conversion of solid state to liquid state is called fusion. What is meant by the latent heat of fusion?

Hint: This question is based on the concept of conversion of solid state of a substance to its liquid state. This process involves absorption of heat energy that helps to break the bonds in solid state. As a result the substance breaks down and becomes a liquid. This process is called fusion.

Complete answer:
Melting is the transformation of a solid into a liquid. (An older word you can come across is fusion.) Liquefaction is the process of changing a substance to liquid state. The temperature at which a pure material melts (also known as the melting point) is a property of that substance. The transformation of a solid into a liquid necessitates the use of energy.
To transition from a solid to a liquid, any pure substance requires a certain amount of energy. When solids are heated to the point that the molecules that keep their bonds together break apart, a liquid is formed. Solid ice melting into liquid water is the most common example. Melting, also known as heat of fusion, is a mechanism that causes the molecules in a material to become less coordinated.
The amount of energy that must be supplied to a solid material (typically in the form of heat) in order to cause a change in its physical state and turn it into a liquid is known as latent heat of fusion (when the pressure of the environment is kept constant). The latent heat of fusion of one kilogram of water, for example, is 333.55 kilojoules, which is the amount of heat energy that must be supplied to convert 1 kg of ice without increasing the environment's temperature (which is held at zero degrees Celsius).

Note:
The heat of solidification, which is the amount of energy that must be supplied to a liquid in order to allow a phase change and the conversion of the liquid into a solid, is the polar opposite of latent heat of fusion. The latent heat of fusion is always equal in magnitude to the heat of solidification of a material, but it always has the opposite symbol.