Difference between acronym and abbreviation

Be aware of the difference between an acronym and an abbreviation.
Remember, an acronym is a combination of letters making a word that you can
pronounce as a word. For example UNICEF is an acronym for United Nations Children's Fund. One kind of an abbreviation, however, is a set of uppercase
letters (without periods) that you can pronounce only as letters and never
as a word. Examples are CBS (C-B-S), NFL (N-F-L), YWCA (Y-W-C-A), and
AFL-CIO (A-F-L, C-I-O).

Gareth Roberts maintains a list of acronyms / abbreviations related to Apps on his blog here.