What's a sump?

On Long Island, at least where I was from, there are huge holes dug into the ground, surrounded by fences topped with barbed wire, that serve as drainage ditches for the surrounding neighborhood. They also served as a place for punky kids to burn stuff, smoke, break bottles, sled, drink booze and, in general, participate in things they ain't supposed to be doing. This is the gate to the sump just a few hundred feet down the street from 976 Cheryl Dr., just as I remember it.