Melting and fusion are not the same thing, although both melting and fusion share a connection with each other.
Melting is required for fusion to happen.
Melting is the process of a solid turning into a liquid and fusion is when the melted solid that turned into liquid cools down and hardens again and melts onto another surface.
Fusion can also refer to nuclear processes where atomic nuclei combine, which is a different phenomenon.
The word fusion which is a noun comes from the Latin word fundere, meaning melt, so fusion is the act of melting things together.
In science, fusion is the process of merging atoms together to create energy.
Fusion is also used as an adjective.
Fusion cuisine is the combination of at least two different ways of cooking.
The phenomenon is called fusion because when two separate solid objects made from the same substance are melted, they can get mixed together into a new one (they fuse).
This can also apply to different substances, like alloys from different metals or mixtures of alcohol and water, or different waxes and oils.