If we wanted to denote millions, we would show that as MM. For this, we should credit the Romans. M is the Roman numeral for thousand and MM is meant to convey one thousand-thousand — or million. To take it further; one billion would be shown as $1MMM or one-thousand million.

In a medical connotation, MM may represent multiply myeloma or molecular medicine. On a financial statement, you can express $1 million as $1MM to provide more clarity when you present these numbers to your accounting department and senior management.

In finance and accounting, MM (or lowercase “mm”) commonly denotes that the units of figures presented are in millions. The Roman numeral M denotes thousands. In this context, MM is the same as writing “M multiplied by M,” which is equal to “1,000 times 1,000,” which equals 1,000,000 (one million).

Why is there such a difference in terms when they basically mean the same thing? K comes from the Greek world "kilo" which means one thousand and is used in metric / decimal systems. The corresponding prefix for one million is M. An amount in the accounting and financial world shown as $14K would equate to $14,000.00.