1. A series of gears in a car, a truck, etc. that allows for the rear wheels to turn at different rates; such as, for turning a corner: After the accident, Sandy had to replace the differential in his truck because it was damaged.
2. The distinguishing degree of not being similar to another person or items: There was a considerable differential in salaries between the newly hired salespeople and the those with years of experience.

Although there was an obvious price differential between the two cars, Samuel and Gertrude decided it was worth it to get the one that had more safety features.