Alleys

n: The two rectangles, 4 feet 6 inches wide and 78 feet long, that border each side of a tennis court. In singles, they don't come into play at all, and are disregarded. They are very important in doubles, which is why they exist. Without having to cover that extra 9 feet of width, 2 good doubles partners could so dominate the net that it would be virtually impossible to pass them.