It comes from finance - the rest of us just use "M" for million. I believe it's from Roman numerals (MM = thousand * thousand).

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conductr 3 days ago | parent | next [-]

I’m in finance and exclusively use the M and K to reference millions and thousands. Everyone says the MM is more accurate and I get that from a Roman numeral perspective it may be (if you ignore that it actually means 2000), yet I’ve never once encountered anyone using M as a thousand in the writing or reading of financial figures. I think it’s primarily a financial news, journalism/writing style, I rarely see it in business at all. Sometimes I see MM from the PE/banker guys and that’s about the only time I see it IRL.

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chowells 3 days ago | parent [-]

Ok, I see where the "actually 2000" misconception would come from. A mile is 2000 steps, and "mile" comes from "mille".

But "mille" means 1000. Specifically, it was the distance covered by 1000 paces from a marching Roman soldier. It's more consistent to measure paces than steps in the face of left/right asymmetries, so it's the unit implied when you just say you're marching 1000.

	▲	conductr 2 days ago \| parent [-]
		MM literally translates to 2000 in Roman numerals and Roman numerals is always the reason provided for why MM is used for millions. I don’t see where mille or it’s history of steps gets into the picture at all, unless it’s the real reason for MM being million and everyone’s explanation is just wrong (they effectively don’t know why they’re using MM). It still kind of reasons that if the idea for MM is to be more precise/clear than M, they’ve not done a very good job picking a clearer abbreviation.

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IndrekR 3 days ago | parent | prev [-]

The funny thing is, that MM in roman numerals means 2000.