Fusion is the process of combining two or more things together into one. If your favorite genres are Westerns and reality dating shows, maybe when you become a TV executive, you'll create a fusion of the two, where competing dates have shoot-outs in saloons.
The noun fusion 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. Fusion music is usually the combination of jazz and rock.