Difference between an acronym and abbreviation?

Solution 1:

An acronym (as the term is commonly used) is a term that is formed from the initial letters of some longer name and is pronounced differently than the expanded form. Examples of acronyms as the term is commonly used:

• FBI, which stands for Federal Bureau of Investigation, but is pronounced ef-bee-I
• NATO, which stands for North Atlantic Treaty Organization, but is pronounced NAY-toe
• IUPAC, which stands for International Union of Pure and Applied Chemistry, but is pronounced I-U-pak

An abbreviation is written differently from the expanded form but is pronounced the same. Examples:

• Mr., which stands for mister and is pronounced mister
• ft., which stands for feet and is pronounced feet
• etc., which stands for et cetera and is pronounced et cetera

Whether the form is pronounced as a “word” or as letter names or as some combination of the two is a red herring. The key difference is whether the abbreviated form is pronounced differently from the expanded form.

Solution 2:

An acronym is a type of abbreviation that is pronounced as a word (e.g. SCUBA, LASER).

The following article is worth a look:

The Difference Between Acronyms and Abbreviations (and Acrostics)