That definition is essentially equivalent to the others.
The point is that some people incorrectly use the word "acronym" to
refer to abbreviations that are formed from initial letters, but are
not pronounced as words (such as AFL-CIO, NAACP, and so forth).
None of the definitions quoted in this thread mentioned
pronunciation at all. In addition, according to Merriam-Webster
(Word for the Wise, August 28, 1997):
``It's possible to divide acronyms into initialisms, initial
letters pronounced with letter names, and word acronyms,
pronounced as words. We think the division doesn't need to be so
sharp and prefer to think of particular acronyms as falling
somewhere along a spectrum.
``At one extreme are terms that show their alphabetic
origin, like TB (for tuberculosis) and PDQ (for pretty damned
quick). Sometimes, as with TNT, folks are more familiar with the
acronym than with the source word (in that case, trinitrotoluene,
the compound in the explosive).''
Source:
http://www.m-w.com/textonly/wftw/97aug/82897.htm
Tak-Shing