A surge protector (or surge suppressor or surge diverter) is an appliance or device designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold.
When a threshold is over 120V, a surge protector shorts to ground voltage or blocks the voltage. Without a surge protector, anything higher than 120V can create component issues, such as permanent damage, reduced lifespan of internal devices, burned wires and data loss.
A surge protector is usually installed in communications structures, process control systems, power distribution panels or other substantial industrialized systems. Smaller versions are typically installed in electrical service entrances located office buildings and residences.
An example of a surge protector: (brand APC)