According to Welding Engineer, MIG welding is a "semiautomatic welding process," referring to the fact that metal wire is fed from a spool to the welding point. The wire (electrode) melts and creates filler metal between the objects that are being welded together.
The MIG welding method offers a number of benefits, making it ideal for certain applications. MIG welding produces higher deposition rates than other types of welding. Tooling U defines "deposition rate" as "the rate at which an electrode melts into the molten weld puddle to form a weld." Long welds are facilitated through MIG welding because frequent starting/stopping is not required. Also, very little cleanup is needed after MIG welding.
MIG welding requires the use of a shielding gas to prevent contamination at the weld point as well as to stabilize arc movement. Argon is the most widely used shielding gas for MIG welding. In certain cases, argon is combined with carbon dioxide or oxygen.