What's the difference between an abbreviation and an acronym?

Some people are unsure of whether to call ASAP or appt abbreviations or acronyms. Both abbreviation and acronym are used to refer to a shortened form, but an acronym is a shortened form of a phrase and is usually made up of the initial letters of that phrase. For example, NATO comes from “North Atlantic Treaty Organization,” and ASAP comes from “as soon as possible.” Abbreviations, on the other hand, can be shortened forms of words or phrases, and need not necessarily be made up of the initial letters of either. ASAP and appt (for appointment) are both considered abbreviations, but only ASAP is an acronym. Acronyms are a type of abbreviation.