Gas metal arc welding, or GMAW, uses an electric arc formed between metal and wire electrode. A continuous solid wire electrode is sent through the gun and a shielding gas protects the process from contaminants in the air.
SMAW, on the other hand, uses a flux-covered electrode that produces a gas shield when heated, so it doesn’t rely on an external gas like GMAW. SMAW welders also require new electrodes periodically, while GMAW has a wire electrode fed automatically.