These types of air conditioners are ductless systems, and in general are used to cool or heat a single room at a time. More than one air conditioner can be installed to air condition multiple rooms.
Wall split air conditioners come as 2 separate units which are closely adjoined. One unit is installed on the exterior portion of the wall, while the other is mounted on the interior wall of the room that is being air conditioned.
Choosing this type of air conditioner is the easiest way to cool or heat a single room.