Rocker switch covers are a type of cover that protect a rocker switch. A rocker switch is a variety of switch that rocks back and forth, meaning while one end is depressed the other is neutral (not pressed); one side of the switch is always on and the other is off. These are often marked with a "1" for on and "0" for off.
A rocker switch has independent circuitry which means that a light is visible on the face of the switch in both the on and off positions, allowing the switch to be found easily in the dark. With dependent circuitry, the light would be activated only when the switch is on. Many common household switches are rocker switches.
Rocker switch covers protect the rocker switch from workshop dust and grime. They are also often splash proof, fitting securely over the rocker switch to provide protection against water damage.