Electrical resistors, which are voltage-dependent, are called varistors (variable resistor). Variable because at a certain voltage (threshold voltage) the differential resistance suddenly becomes smaller. Varistors are also abbreviated to VDR (voltage dependent resistor) or MOV (metal oxide varistor). The components are characterized by a high durability against repeated high pulse currents.
For a varistor to optimally fulfill its primary function as overvoltage protection (high energy absorption capacity, rapid response to voltage peaks), it must be optimally designed for its field of application (type and extent of overvoltage situations, acceptable forward voltage, safety standards, etc.).