M is the Roman numeral for one thousand. In the financial press, MM is M*M or one million. I've also seen it used with BTUs. Some cultures (UK?) actually do/di

M is the Roman numeral for one thousand. In the financial press, MM is M*M or one million. I've also seen it used with BTUs. Some cultures (UK?) actually do/did use M in the Roman sense to mean thousand, so 33M would mean 33 thousand. That conflicts with metric Mega 10e6, so K is becoming more popular. In Rome of course, MM would be two thousand. In short, it's complicated. Or at least context-sensitive.