If something's fused, it's connected or joined to something else. Fused wires have been soldered together, and fused families are connected through love, marriage, or children.
When two things are fused, they become one fused whole — permanently attached and combined. Fused glass jewelry or ornaments consist of different colors combined through heat, and fused vertebrae result from a reparative surgery that connects them to each other to combat back pain or other spinal conditions. Fused comes from the verb form of fuse, "join, blend, or heat," from the Latin fusus, "melted."