[This is a fast-access FAQ excerpt.]
Strictly, an acronym is a string of initial letters pronounceable
as a word, such as "NATO". Abbreviations like "NBC" have been
variously designated "alphabetisms" and "initialisms", although some
people do call them acronyms. WDEU says, "Dictionaries, however,
do not make this distinction [between acronyms and initialisms]
because writers in general do not"; but two of the best known books
on acronyms are titled Acronyms, Initialisms and Abbreviations
Dictionary (19th ed., Gale, 1993) and Concise Dictionary of
Acronyms and Initialisms (Facts on File, 1988).
The Network Dictionary of Acronyms is available through World Wide
Web ([...]) or by e-mail (send the word "help" to [...]).
[The addresses given are no longer current.]