In informal conversation, many people call both URL and
RAM acronyms, but in strict usage, only RAM (which is
pronounced as the single word) is an acronym. URL (which is pronounced
as separate letters (you-are-el) is an initialism. Both represent a
longer phrase and are composed of the initial letter of each word in the phrase
they represent:
uniform resource locator
random access memory
For some acronyms and initialisms, not every word in the phrase is
represented:
ASCII (American Standard Code for Information Exchange)
and in others, two or more letters are used from some of the words:
NORAD (North American Air Defense)
Let's look at several writing style issues concerning the use of acronyms and initialisms. Overuse is the one I find most irksome. I have seen paragraphs with more than 20 acronyms and initialisms and pages with over 60. This looks a bit like someone has spilled alphabet soup on the manuscript or like the caps key had a poltergeist. Online, it can seem like shouting. Printed or online, a dense concentration of acronyms and initialisms can make reading very cumbersome.
Since the object of using these abbreviated forms is to make copy easier to read and less cluttered, resist using an acronym or initialism for every phrase that has one. A good rule to follow is to include them only if the phrase is used frequently in the document or several times on one page. Use them for less frequently used phrases only when the shortened form is much more common among your potential readers than its definition is--for example, YMCA, ZIP Code, or CPU.
This brings us to our next writing style issue--making sure that your readers understand your terminology. In some cases, the abbreviated form is so common and its word-by-word definition so little known, like ASCII, that a definition may not be necessary or a generic definition may be more appropriate. However, because acronyms and initialisms can have multiple meanings (like IDE and SST), it's a good idea to define each the first time it occurs in a document. Most of the time, the definition should be given first, with the shortened version following in parentheses or surrounded by commas. When the shortened version is much more common than its definition (e.g., RISC or BASIC), the definition can be given in parentheses following the acronym or initialism.
In the definitions, it is unnecessary to underline or italicize the letters
that make up the shortened form. Instead of helping your readers, this can just
make the copy look cluttered. Use capital letters in a definition only if it is
a proper noun:
National Aeronautics and Space Administration
Space Shuttle Main Engine
Icing Research Tunnel
random access memory
traveling wave tube
file transfer protocol
Most acronyms and initialisms are written with all capital letters, but this can change over time. Some, like scuba and modem, have become so common that they are now treated like words instead of acronyms. A few, like Landsat and Conrail, are written with initial capital letters. It is usually acceptable to start a sentence with an acronym or initialism that begins with a capital letter.
Indefinite articles are used in the same way as for standard words, but their
use can seem trickier:
An is used if an acronym or initialism begins with a vowel sound:
an SOS signal (SOS begins with the short e
sound: es-oh-es)
But a is used if an acronym or initialism begins with a consonant
sound:
a UFO sighting (UFObegins with the y sound:
you-ef-oh)
Which is correct? a NASA-funded project or an NASA-funded project?
It depends on how you think your readers will pronounce NASA. Some people say en-ay-es-ay, which starts with a vowel sound, so an NASA project would be correct. Others say nah-suh, which begins with a consonant sound, so a NASA project would be correct.
Our final writing issue is how to form possessives and plurals from acronyms
and initialisms. To show possession, just add 's to the end of the
abbreviated form:
NASA's next shuttle launch
If the acronym already ends in S, add ' or recast the
sentence:
the MAC OS' features
features of the MAC OS
For plurals, many style guides suggest just adding a lowercase s
to an all-capital-letter acronym or initialism. However, the Government
Printing Office Style Manual, which NASA follows, requests that plurals be made
the same way as possessives, by adding 's:
Employees were warned of possible RIF's at two different Government
agencies.
To sum up our recommendations, use acronyms and initialisms when a document
is cluttered by the repeated use of a few key phrases or when the shortened
forms are more familiar than their definitions. Do not burden your readers with
unnecessary acronyms and initialisms, especially if they are only used a few
times. Finally, do not assume that all your readers will be familiar with your
group's jargon. Define all of your abbreviated forms the first time that
they occur in a document.
Stumped by an undefined acronym or initialism? Look it up
online.
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[Privacy Policy and Important Notices]
Responsible NASA Official: Sue.E.Butts@nasa.gov,
Glenn Technical Publications Manager
Web Curator: Caroline.A.Rist@nasa.gov
(Wyle)
Last updated: 1/20/2009