A varistor is an electronic component with a significant non-ohmic current-voltage characteristic. The name is a portmanteau of variable resistor. Varistors are often used to protect circuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from the sensitive components.
A surge suppression device used to absorb transients and spikes occurring on the power lines, thereby protect electronic equipment plugged into that line. Frequently, the term MOV (Metal Oxide Varistor) is used instead.