The fascia boards are the part of the roofline which faces straight out from the house and create a border just under the outer edges of the roof eaves. The fascia boards protect the interior structure of the roof from the elements and provide an aesthetic embellishment to the roof. They support the lowest row of roof tiles and are also the part of the roof to which the guttering is attached.
Fascia boards are traditionally made from wood but these days can also be uPVC or metal. Wood can be hard to beat on aesthetics but uPVC offers more durability and weather resistance.
Depending on the type of roof and house design the fascia boards can extend all around the house or just on a couple of sides.