A corresponding unit of area is the square millimetre and a corresponding unit … In accounting speak, a written "MM" means a million, whether the accountant is referring to units, dollars, euros or shares. Rather than writing $400,000,000 or $400 million, the accountant can use the MM abbreviation and write $400MM instead. MM: Magnetic Meridian (surveying) MM: Mysore Mallige (rice variety) MM: Mortimer Mouse … MM: Mobility Management: MM: Moving Mean (statistics) MM: Mystery Man: MM: Magister Militum (Latin: Military Instructor, epigraphy) MM: Magic Missile (Dungons & Dragons) MM: Media Molecule (game maker) MM: Mickey Mantle: MM: MuchMusic (TV channel) MM: Master of Management (degree) MM: Miva Merchant (ecommerce) MM: MathMagic (software) MM: Mother's Milk (Red Chili Peppers … You have to be careful when using it or interpreting it because MM can stand for other things too. A millimetre (American spelling: millimeter, symbol mm) is one thousandth of a metre, which is the International System of Units (SI) base unit of length. The millimetre is part of a metric system.