A duplex receptacle has removable metal tabs that electrically connect hot and neutral together on each receptacle. A split receptacle is a duplex with one or both tabs removed to isolate each receptacle from the other. In most cases, only the hot 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 receptacle in the house for identification. The tab on the receptacle that connects the hot terminals together is removed so that each half of the receptacle can operate in dependently.
Tab is removed
Neutral terminal screws connected by metal tab
Split receptacle rotated 180 deg from conventional orientation