Final answer:
Coping is the material at the top of a parapet wall that serves as a protective cover and prevents water penetration.
Step-by-step explanation:
The material at the top of a parapet wall is known as coping. Coping serves as a protective cover for the wall and helps to prevent water penetration into the underlying structure. It can be made of various materials such as stone, concrete, metal, or brick, depending on the design and requirements of the wall.