Abbreviation vs. Acronym

Oxford English Dictionary

• Abbreviation: A shortened form of a word or phrase.


• Acronym: A word formed from the initial letters of other words (e.g., laser, which is an acronym of Light Amplification by Stimulated Emissio of Radiation).


• Initialism: An abbreviation consisting of initial letters pronounced separately(e.g., BBC).
  

all acronyms and initialisms are abbreviations, but not all abbreviations are acronyms or initialisms.