Some disagree that acronyms are any different than abbreviations. To them, all acronyms are abbreviations and all abbreviations are acronyms.
For instance, I found this statement on the Acronym Server web site: "There is no requirement that an acronym be pronounceable as a normal word (this is a curious myth perpetuated by American dictionaries): IBM is just as much an acronym as LASER."
A short time ago I might have agreed with this statement, but now I do not. First, I don't believe American dictionaries are incorrect in saying that an acronym is a word formed from the first (or first few) letters of several words.
Also, it seems to me that words with similar prefixes ought to carry similar meanings. So let's compare the word "acrostic" with "acronym." Since they have the same prefix, they ought to carry similar meanings.
We've already seen what acronym means. An acrostic is a poem or series of lines in which certain letters, usually the first, form a name or motto. Thus:
"TREE" by Ryan Healy
The branches stretch wide overhead,
Revealing patches of blue through the green.
Everyone should lie down beneath a tree and
Enjoy the view from here.
I just scribbled that out to give you an example of what an acrostic looks like. Now, could you imagine if someone made the argument that the first letters of the poem didn't have to form a word or pattern to be an acrostic? Then, all of a sudden, all poems ever written would be acrostics!
I argue that for a poem to be an acrostic, it must spell out a word or follow some kind of pattern (like ABC). And I argue that for an abbreviation to qualify as an acronym, it must form a pronouncable word. So SCUBA qualifies and NFL does not. (Can you prounounce that? "Niffle..." Just kidding.)
An Acronym Guide reader, T. Carter Ross, wrote to me 12/14/2004 to make the case that there are actually three different ways of shortening words, instead of the two I've suggested.
First, there are abbreviations. An abbreviation is merely the shortened form of a word. Acronyms and initialisms are specific types of abbreviations, says Carter.
Basic abbreviations are pronounced like the full word it represents. So "St." is pronounced "Street" (or "Saint") and "Ct." is pronounced Court and "Mr." is pronounced "Mister," etc. These basic abbreviations are usually followed by a period.
An initialism is a type of abbreviation pronounced one letter at a time. For instance, PGA, AARP, IOU, etc.
Finally, as I suggested above, an acronym is a type of abbreviation that is pronounced as a word. For instance, SCUBA, LASER, PUSH, etc.
Thanks to Carter for further refining my understanding of shortened words.