1) Board blemish 2) Board feature 3) Board imperfection 4) Eyehole 5) Flaw in a fence 6) Flaw in a floor board 7) Hole 8) Imperfection in a board 9) Imperfection in lumber 10) Keyhole 11) Lumber blemish 12) Small hole 13) Spy-hole 14) Tough spot 15) Vantage point 
[n] - a hole in a board where a knot came out
a hole in a board or plank formed by the falling out of a knot or a portion of a knot.