A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions, a form of soft key. On some keyboards/computers, function keys may have default actions, accessible on power-on.
Surge definition, a strong, wavelike, forward movement, rush, or sweep: the onward surge of an angry mob. See more.
A varistor is able to short these surges and spikes and keep them away from the following application. A varistor is also known as Voltage Dependent Resistor or VDR. A power surge or a spike is an increase in voltage significantly above the standard voltage of 230 volts.