I think you're getting the definition of acronym mixed up with that of abbreviation. An acronym is an initialism that is pronounced as if it is a natural word.

I think you're getting the definition of acronym mixed up with that of abbreviation. An acronym is an initialism that is pronounced as if it is a natural word. For example, NASA is both an initialism and an acronym. FBI is an initialism, but not an acronym. Well that's the dictionary definition anyway. In practical terms, I think most people use acronym as a synonym of initialism, at least in the US. This is one of the places where the dictionary definition doesn't match with real world usage.