A duplex receptacle has removable metal tabs that electrically connect the two terminals together on each side of the receptacle. A split receptacle has one or both tabs removed to isolate each terminal from the other. In most cases, only the line tab is removed.
Switched Split Receptacle
A switched split duplex receptacle (also known as a “half hot”) is used to control a table or floor lamp with a wall switch near the room entrance. Half of the duplex is connected to the switch and the other half is always hot. Switched duplex receptacles are rotated 180 degrees from the orientation of other receptacles in the house for identification. The tab on the receptacle that connects the line terminals together is removed so that each half of the receptacle can operate independently.
Split Receptacle, Same Circuit
Split Receptacle, Different Circuits
Split receptacle rotated 180 deg from conventional orientation