MO—it’s a multifunctional set of letters. MO is commonly used as an abbreviation for modus operandi, meaning “mode of operating or working.” It’s also commonly a postal abbreviation for Missouri.

You may not always encounter mo in uppercase letters in informal contexts in digital communication. So, two other widespread, popular uses of mo you may encounter are: Mo, a guy’s name, and mo, a dialectical pronunciation of more.

In the U.K. and other English-speaking places around the world, mo is a slang shortening of the word moment.

How is MO pronounced?

What are some variants of MO?

or M.O. or mo’ or mo

What are some other words related to MO?

• more
• modus operandi
• Missouri

The acronym MO is short for modus operandi, an expression directly from Latin meaning “way of operating.” Modus operandi was first recorded in English by the 1650s. The phrase specifically refers to the particular, often characteristic manner someone goes about doing something—later broadened to one’s “style.”

Modus operandi was adopted by early 20th-century criminologists who sought to establish patterns in crimes. These researchers identified criminals on their methods, called the modus operandi system, shortened to MO. As any fan of TV police procedurals can tell you, MO spread as an expression for a criminal’s signature pattern of committing the crime.

Starting in 1831, Mo. was the official postal abbreviation for the state of Missouri, written as MO by 1963.

Mo is also a short form of the common men’s name Muhammad or Mohammed, borne by the likes of the great British-Somali runner Mo Farah.

Furthermore, or should we say furthermo’, mo’ is a pronunciation of more in Black English, which often drops word-final Rs. (English once had, in fact, a word mo that meant “more.”) Mo’ reached the top of the Billboard charts thanks to the Notorious B.I.G.’s 1997 hit song “Mo Money Mo Problems.”

In British slang, mo is also a slang shortening of moment, as in I’ll call you in just a mo!

MO is a go-to shorthand for modus operandi to describe someone’s style or manner of doing things, e.g., His MO is going to coffeeshops to get his writing done.

Using mo’ for more is common in Black and Southern American English. As rapper Kendrick Lamar raps on his 2017 “XXX.”: “Johnny said books ain’t cool no mo’, no mo’.”

As the official abbreviation for Missouri, MO is very useful when addressing things to or from there.

And as Muhammad is one of the most common men’s names in the world, expect to meet lots of men who go by Mo for short.

Finally, if you’re in the U.K., drop a casual mo for moment if among friends.

More examples of MO:

“Pastry chef shows you his M.O. in the kitchen”

—Inger Sandal, Arizona Daily Star (headline), April 2010