An acronym is a word or name formed from the initial components of a longer name or phrase.
An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial letter of each word in all caps with no punctuation.
For some, an initialism or alphabetism, connotes this general meaning, and an acronym is a subset with a narrower definition: an initialism pronounced as a word rather than as a sequence of letters. In this sense, NASA is an acronym but USA is not.
The broader sense of acronym, ignoring pronunciation, is its original meaning and in common use. Dictionary and style-guide editors dispute whether the term acronym can be legitimately applied to abbreviations which are not pronounced as words, and they do not agree on acronym spacing, casing, and punctuation.
The phrase that the acronym stands for is called its expansion. The meaning of an acronym includes both its expansion and the meaning of its expansion.