Fusion seems to have contradictory meanings. Technically, it means to melt a solid into a liquid. It comes from the Latin word fundere meaning to pour. But when you weld two rods of metal together you are said to fuse them. When a writer blends two different styles, he is said to fuse them together. How are these two meanings reconciled? The implicaiton in the welding and literature examples is that part of the objects are melted before joining them together. Thus fusion refers to the process of melting. The heat of fusion is the energy that it takes to melt one gram of a solid into a liquid at its melting point.