Final answer:
A separate piece attached to the rear edge of a countertop, designed to protect the wall from splashes, is called a backsplash.
Step-by-step explanation:
The piece attached to the rear edge of a countertop is known as a backsplash. This serves not only as a design element but also helps protect the wall from splashes and stains, particularly in areas where there is a lot of moisture or food preparation, such as kitchens and bathrooms. Therefore, the correct answer would be d. backsplash.