Home/Technical Glossaries/M-Code M-Code G-code (or G programming language) is the street name for the most widely used numerical code programming language. Utilized mainly in automation, G-code is sometimes called G programming language. Very simply, G-code tells computerized machine tools - like laser systems - what to do and how to do it. For example, how fast to move, what path to take, etc. M-code (for “miscellaneous function”) is an auxiliary command; descriptions vary. Many M-codes call for machine functions like “open workstation door,” which is why some say “M” stands for “machine”, though it was not intended to.