An acronym is a type of initialism, which is itself a type of abbreviation.
So acronyms are initialisms where you pronounce the letters like a word (e.g., RAM), initialisms are abbreviations made by taking the initial letters of multiple words and concatenating them regardless of how it's spoken (e.g. FBI for Federal Bureau of Investigation), and an abbreviation is any shortening of a word or phrase into something shorter (e.g., "abbrev." for abbreviation or "US" for United States).
I did some research, and apparently, "United States" without "of America" could be a kind of ellipsis. But more likely, it's just an alternative country name.
So I think that makes US an initialism (because you pronounce it as [yu-es]) for an alt (bonus info: this is a final clipping, or apocope, of "alternative") name.
Other way around.
An acronym is a type of initialism, which is itself a type of abbreviation.
So acronyms are initialisms where you pronounce the letters like a word (e.g., RAM), initialisms are abbreviations made by taking the initial letters of multiple words and concatenating them regardless of how it's spoken (e.g. FBI for Federal Bureau of Investigation), and an abbreviation is any shortening of a word or phrase into something shorter (e.g., "abbrev." for abbreviation or "US" for United States).
Is US an abbreviation of an initialism (USA)?
I did some research, and apparently, "United States" without "of America" could be a kind of ellipsis. But more likely, it's just an alternative country name. So I think that makes US an initialism (because you pronounce it as [yu-es]) for an alt (bonus info: this is a final clipping, or apocope, of "alternative") name.
Linguistics is such a dirt hut...