The most accurate, but cumbersome description would probably be the fair/foul line and pole, as they mark the border between the two.
It's purely arbitrary, of course, that a ball that hits the pole is fair in baseball. In football, a field goal attempt that hits the upright and bounces back is no good. As is a shot that hits the post in hockey. In those sports, it has to carom off the post and into fair territory.