M=Mille. It's used in financial jargon. A mille is also 1000. I never use a single 'M' by itself when talking about money because it's ambiguous. Mega or mill

M=Mille. It's used in financial jargon. A mille is also 1000. I never use a single 'M' by itself when talking about money because it's ambiguous. Mega or mille? If you see MM, it's not ambiguous.