A more thorough explanation:

Definition: A factor that plays a part in producing a result, although it is not the primary cause.

Example: In a car accident, the driver's speeding may be the primary cause of the crash, but the fact that the other driver was distracted by their phone could be a contributing cause.

This example illustrates how a contributing cause is a factor that adds to the primary cause of an event. In this case, the distraction of the other driver added to the primary cause of the accident, which was the speeding of the first driver.