electrode
/ ih-LEK-trohd /
Picture the two metal terminals of a battery, or the two strips dipped into a tank where water is being split into hydrogen and oxygen. Each one is an electrode: a solid conductor that you dip into a solution (or melt) so that electrons can cross the boundary between the wire and the chemistry.
An electrode is the meeting place where electron flow in a wire turns into a chemical change in the liquid. At one electrode, substances give up electrons (oxidation); at the other, substances accept them (reduction). The electrode where oxidation happens is the anode; the one where reduction happens is the cathode. Electrodes are usually made of metals or carbon — sometimes inert, just shuttling electrons, and sometimes taking part in the reaction themselves.
Why care which is which? Because the labels tell you the direction of everything. Knowing the anode and cathode tells you which way electrons flow, which substances are consumed, and where a deposit will form when you electroplate. A useful caution: anode and cathode are defined by oxidation and reduction, not by plus or minus, and the sign actually swaps between a battery (galvanic) and an electrolysis setup.
In electroplating a spoon with silver, the spoon is one electrode (the cathode) where silver builds up, and a bar of silver is the other (the anode) that slowly dissolves to replace it.
Two electrodes: one where metal deposits (cathode), one where it dissolves (anode).
Memory aid: "AN OX" and "RED CAT" — ANode is OXidation, REDuction is at the CAThode. This holds in every cell, even though the +/- signs differ between galvanic and electrolytic ones.