An OZONE hole is a region in the Earth's stratosphere where the concentration of OZONE molecules is much lower than normal. A PEEP hole is a small opening in a door or wall, usually covered by a lens, that allows someone to look through from one side to the other. A PORT hole is an opening in the side of a ship or aircraft, typically round or oval, for light and air to enter, or for passengers or crew to look out of. Therefore, the term 'kind of hole' can refer to any of these three types of holes.