Acronyms and Initialisms–What’s the Difference?

We All Use Acronyms and Initialisms

Today I hope to enlighten the world like Lady Liberty on the difference between acronyms and initialisms. My colleagues in education often joke that our realm is all about acronyms. I used to laugh at that until I sat down one day and tried to list all the acronyms for departments and programs used on our campus. Writer’s cramp forced me to stop before I’d gotten halfway through. But the joke was on me when I discovered that there are acronyms and there are initialisms and, although similar, they are technically not the same.


Acronyms are abbreviations of multi-word nouns, consisting of the initial letters of each word and are pronounceable words. That last phrase is key. For example, the National Aeronautics and Space Administration is universally known by its acronym NASA, and “Light Amplification by Stimulated Emission of Radiation” is the mouthful better known by the acronym laser.

The acronym, like its cousin the initialism, is generally written all in caps with no periods, unless it’s a word like laser, or scuba, or snafu. (Don’t look up that last one unless you’re over eighteen.) Remember the “no periods” part. I still kick myself for missing S.T.E.M. (Science, Technology, Engineering, and Math) in a document I copyedited for a PR specialist a few years ago.[1]


If the abbreviation is not pronounceable as a word, it’s an initialism. We pronounce each letter individually. The familiar combinations FBI, CIA, and IBM are initialisms and not, strictly speaking, acronyms.

So I discovered that the majority of abbreviated departments and programs on my campus were actually initialisms, such as EOPS (Extended Opportunity Programs and Services, not to be confused with EOP—Educational Opportunity Program), DSPS (Disabled Students Programs and Services), and CGE (Continuing and Global Education). I  always tried to be cagey and make that one a true acronym (CAGE) because of the and in there, but it wasn’t appreciated. This discovery of the difference between acronyms and initialisms was, to me, a revelation of near-biblical proportions.

Usage Tips

Here are a few tips for writing acronyms and initialisms. First, go easy with them, especially if you write for a technical or scientific field. Too many abbreviations makes an essay clunky, and people won’t want to read it—just like they don’t want to read essays on grammar and language.

Next, in formal writing it’s best to write out the acronym or initialism on its first occurrence if it’s likely to be unfamiliar to some readers. So I might write out “Food and Drug Administration” the first time and then in subsequent references use its initialism, FDA. If it’s a well-known abbreviation, there’s probably no need to spell it out. NASA is a good example, or JPEG, which is an interesting combination of initialism (J) and acronym (PEG).[2]

Then, it’s important to know which indefinite article should precede an acronym or initialism—whether a or an. Referring to a medical doctor, should it be “a MD” or “an MD”? It’s decided by how the abbreviation is pronounced, whether with an opening consonant or vowel sound. “MD” is pronounced “em-dee,” an opening vowel sound, so the correct article to use is an: “an MD.”

Last, periods are rarely needed with these things today. So it’s DNA, CGI, IRS, HMO, VFW, and USA. Even two-letter abbreviations need no periods, like BA, MA, MD, or US, all of which routinely appeared with periods in the past (B.A., U.S., etc.). One caveat: if the organization you’re writing about uses periods in their own acronym, then you should, too. You don’t want to irritate your teacher or client.


If this has been helpful, feel free to share it. Comments are welcome, too.

(If you’re wondering what the puppy photo has to do with this post—well, nothing, really. I just liked it and wanted to use it—as an experiment of sorts.)

[1] I debated with myself about leaving the periods in and finally decided to do so—but further research revealed I should have suggested STEM, without the periods. Little things like that keep copyeditors awake at night.

[2] To make it simple, I’ll just call JPEG an acronym if you don’t mind. Thanks.

 © 2018 by Dean Christensen. All rights reserved.

Author: Dean Christensen

Educator, copyeditor, writer, baseball bug, word lover, book hound, guitar picker, classical music aficionado, classic rock 'n' roll and movie buff, sinner, saint, former this, used-to-be that, and future who-knows-what. Every day is an adventure in learning how to make the world a better place--grammatically, anyway.

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