Many people use “acronym” when they should use “initialism” instead.

Problem:
These two words refer to different types of abbreviations.

Explanation:
An “initialism” is formed from the initial letters in the words of a name, with each letter individually spoken.

HIV — from “Human Immunodeficiency Virus” — and NPR — from “National Public Radio” — are examples of initialisms.

An “acronym” is formed from parts of the words in a name and is pronounced as a single word. The parts can be:

• initial letters (e.g., AIDS from “Acquired Immune Deficiency Syndrome”);
• initial syllables (e.g., Interpol from “International police”); or,
• arbitrary parts (e.g., amphetamine from “Alpha-methyl-phenethylamine”).

In case you’re wondering, a “truncation” is the name of the third major type of abbreviation (e.g., Minn. from “Minnesota”).

I believe that the tendency to refer to initialisms as acronyms can be traced to ignorance and to my “Devolution toward Simpler” hypothesis. Many acronyms are constructed with the initial letters in the words of a name, just as all initialisms are constructed, so there’s a natural confusion about these abbreviation terms. Beyond this, though, it’s simpler to say “acronym” than it is to say “initialism”.

Solution:
Use “acronym” when you say the abbreviation as a single word; use “initialism” when you say the individual letters of the abbreviation.