Essentially, components that kick in when a voltage exceeds a certain limit to allow that excess voltage to shunt to ground instead of continue to build up in the circuit.
Similar devices in pneumatics or hydraulics are pressure relief valves [https://en.m.wikipedia.org/wiki/Relief_valve], and they provide similar functionality - giving a easier/lower resistance path for the high voltage/pressure, so delicate things downstream don’t fail.
Essentially, components that kick in when a voltage exceeds a certain limit to allow that excess voltage to shunt to ground instead of continue to build up in the circuit.
Similar devices in pneumatics or hydraulics are pressure relief valves [https://en.m.wikipedia.org/wiki/Relief_valve], and they provide similar functionality - giving a easier/lower resistance path for the high voltage/pressure, so delicate things downstream don’t fail.