MIG welding, or Metal Inert Gas welding, is a type of welding that uses inert gas to protect the weld area from contamination. This process can be done with or without gas, but using gas is often preferable because it can help to prevent oxidation and other types of damage to the weld area.
MIG welding without gas is typically done with a solid wire that is coated with a flux to prevent the weld area from being contaminated.