Gas welding is a process that uses heat generated from burning a combination of different gases to melt and fuse metals.
Gas welding allows for the fusing of both nonferrous (not containing iron) and ferrous metals, plus no requirement of electricity to get the welds going. Oxy-acetylene welding uses a combination of oxygen and a fuel gas (typically acetylene) and is used primarily for welding thin metal sections.
Arc welding is a fusion welding process used to join metals. An electric arc from an AC or DC power supply creates an intense heat, which melts the metal at the join between two work pieces.
Arc welding is commonly used to join materials and is used across a lot of different industries.