Final answer:
The term for multinucleated cells formed from the fusion of host cells during infections is syncytium, characteristic of certain viral infections like RSV.
Step-by-step explanation:
The term that refers to multinucleated cells that form when many host cells fuse together during infections is syncytium. A syncytium is caused by the fusion of normal cells during infections or other processes, leading to a single, large cell with multiple nuclei. This process can be seen in certain viral infections, where the virus-induced fusion of adjacent cells allows the infection to spread directly from cell to cell. An example of such a virus is the respiratory syncytial virus (RSV), which can cause a syncytium in the lungs.