A board fixed to the bottom of a door on the outside to prevent rain driving in.
a board fitted over an open port (or, in this case, deck) to deflect water [369.42
a long thin board with one edge thicker than the other; used as siding by lapping one board over the board below
See fascia, though this term is usually used for diagonal boards rather than horizontal runs where the gutter is fixed to it.
Boards that cover external surfaces and overlap to keep out the rain.