- a set of initials representing a name, organization, or the like, with each letter pronounced separately, as FBI for Federal Bureau of Investigation.
- a name or term formed from the initial letters of a group of words and pronounced as a separate word, as NATO for North Atlantic Treaty Organization; an acronym.
- the practice of using initials or forming words from initials.
Origin of initialism
word formed from the first letters of other words or a phrase, 1957, from initial (n.) + -ism. The distinction from acronym is not universally agreed-upon; in general, words such as NATO, where the letters form a word, are regarded as acronyms, those such as FBI, where the letters sound as letters, are initialisms.