Hello, Noel. Thank you for your question.
An acronym is the subset of Abbreviation. The only difference between Abbreviation and Acronym is that of pronunciation. If pronounced differently than the actual words, it is an acronym. However, if the pronunciation of shortened word is similar to that of the original word, it is an abbreviation.
NATO - pronounced as Nay-toe is an acronym for North Atlantic Treaty Organization.
ft. - pronounced as feet is the abbreviation of feet (a unit of measurement).
I hope that helpled.