As it turns out, for something to be an acronym, it is not enough that it be an abbreviation formed from initial letters. To be an acronym, the abbreviation must be pronounced as a word. Thus for example NASA and ASCII are acronyms, but TYFNIL is not (or at least I have assumed it is not).
So what name may we properly give to an abbreviation formed from initial letters if it is not pronounced as a word? The correct term, it turns out, is “initialism”.
With this gentle reminder from Penn, we can all use the term acronym correctly from now on.
Just to save a few readers from feeling the need to post alternative-point-of-view comments, yes I am well aware that you can find a few sources that say something like:
By now lots of people get this wrong and so we at this dictionary are going to give up and say that the term “acronym” also maybe nowadays includes “initialisms that cannot be pronounced as words”.
Words have meanings and we all benefit when the meanings are observed and preserved. To be correctly termed an acronym, an abbreviation formed from initial letters must be pronounced as a word. If you want to give a name to an abbreviation formed from initial letters that cannot be pronounced as a word, the term is “initialism”.