electrode

In arc welding, the arc is created across a gap between the base metal and the electrode. The base metal is held by a work clamp (ground clamp), and the electrode is held by an electrode holder. Both the clamp and the holder are attached to cables called leads.

Electrodes are either consumable (meaning the filler metal melts from them) or non-consumable (the filler is supplied by a filler rod instead of by the electrode, if filler is used at all).  Sometimes filler rods and electrodes look similar, but the main difference between them is that filler rods are never part of the electrical circuit.

In SMAW (consumable electrode), liquid filler metal from the electrode crosses the gap inside the arc stream to become part of the weld.

In GMAW (consumable electrode), the electrode is a continuously-fed wire that ultimately becomes part of the weld.

In GTAW (non-consumable electrode), the electrode is made of Tungsten, which has the highest melting point of any metal (which is why it's also used for light bulb filaments).