The cathode is the electrode where reduction occurs—the chemical process that involves gaining electrons. This reduction process complements the oxidation at the anode.
Its electrical charge depends on the device: in an electrolytic cell (such as a water electrolyzer or plating bath), the cathode is the negative terminal where electrons are supplied. Conversely, in a spontaneously operating Galvanic cell (a discharging battery), the cathode is the positive terminal, acting as the receiving site for electrons from the external circuit. The defining characteristic is always the occurrence of reduction.