In texting and internet slang, MM can be used as a friendly abbreviation for “make me” during light-hearted conversations. It is not uncommon to come across abbreviations like “TY” (thank you) and “GG” (good game) alongside MM in everyday chat and messaging.

Its definition is: “used to indicate agreement, satisfaction, or encouragement to continue speaking”. In short, it usually means “Yes.” It could be seen as the closed-mouth version of 'uh-huh'. Merriam-Webster cites the first use of 'mm-hmm' as 1934, but the first use of 'uh-huh' as 1858.

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).

“Milli” comes from the Latin word “mille,” meaning one-thousandth. Therefore, a millimeter is one-thousandth of a meter. The symbol of a millimeter is “mm.” In case you are wondering how to measure length in millimeters or how a length of a millimeter or 1 mm looks like, let's check it out on a ruler.