This article defines the terms "acronym" and "initialism" and gives examples of each.
You may know the definition that says that an acronym is a word formed from the initial letters of other words; for example, NASA and RAM. There is some debate, though, whether words like USA and HTML should also be called acronyms. The issue is whether or not you feel that acronyms must be pronounceable as a word.
One camp in this debate argues that words like USA and HTML are acronyms. The other camp argues that they're not because they aren't pronounced as a word but are sounded out one letter at a time. That is, yoo-ess-ay and aitch-tee-em-ell.
This leads us to two different definitions of acronym:
1. An acronym is a word that is formed from the initial letters of other words; for example, NASA and HTML.
2. An acronym is a word that is formed from the initial letters of other words and is pronounced as a word, not spelled out one letter at a time; e.g. NASA.
Here are some examples that everyone should agree are acronyms:
ASCII: American standard code for information interchange
NASA: National Aeronautics and Space Administration
Qantas: Queensland and Northern Territory Aerial Services
RAM: random-access memory
ROM: read-only memory
If you prefer the first of the definitions cited above, you will also think of these words as acronyms:
HTML: hypertext markup language
IBM: International Business Machines
USA: United States of America
WA: Western Australia
What if you prefer the second definition — the one that says that acronyms must be pronounceable as words? What can you call these latter examples if not acronyms?
One term that fits the bill nicely is initialism. The American Heritage Dictionary provides the following definition of this term:
Initialism: An abbreviation consisting of the first letter or letters of words in a phrase (for example, IRS for Internal Revenue Service), syllables or components of a word (TNT for trinitrotoluene), or a combination of words and syllables (ESP for extrasensory perception) and pronounced by spelling out the letters one by one rather than as a solid word.
Distinguishing between acronyms and initialisms in this way is by no means universal. If you like new words, though, this seems like a good one.