Pet door

A pet door or pet flap (also referred to in more specific terms, such as cat flap, cat door, dog door, or doggie door) is a small portal in a wall, window or human door to allow pets to enter and exit a house (or other structure) on their own without needing a person to open the door. Originally simple holes, the modern form is a hinged and often spring-loaded panel or flexible flap, and some are electronically controlled. They offer a degree of protection against wind, rain, and larger-bodied intruders entering the dwelling. Similar hatches can let dogs through fences at stiles. A related concept is the pet gate, which is easy for humans to open but acts as a secure pet barrier.