Final answer:
The white crescent-shaped area located over the nail matrix is called the lunula. It appears white due to the underlying nail matrix being visible.
Step-by-step explanation:
The white crescent-shaped area located over the nail matrix is called lunula. The nail matrix is the area at the base of the nail where new nail cells are produced. The lunula appears white because it is an area of the nail bed where the nail is not densely packed with keratinocytes, allowing the underlying nail matrix to show through.