Final answer:
A fascia or fascia board is the board nailed to the ends of rafter tails, serving as a gutter mounting surface and offering both functional support.
Step-by-step explanation:
A board that is nailed to the ends of the rafter tails and serves as a mounting surface for gutters is known as a fascia or fascia board. This architectural element is not only functional, providing a level surface for gutter attachment, but it also contributes to the aesthetic of a building's exterior by creating a smooth, finished edge along the roofline.
The fascia board is crucial for supporting gutters and protecting the underlying roof structure from water damage. The fascia board is typically made of wood or synthetic material and is attached horizontally to the lower edge of the roof. It provides support for the gutter system and helps to redirect rainwater away from the house.