An acronym is a word or name formed from the initial components of a longer name or phrase, usually using individual initial letters, as in NATO (North Atlantic Treaty Organization) or EU (European Union), but sometimes using syllables, as in Benelux (Belgium, Netherlands and Luxembourg), or a mixture of the two, as in radar (RAdio Detection And Ranging). Similarly, acronyms are sometimes pronounced as words, as in NASA or UNESCO, sometimes as the individual letters, as in FBI or ATM, or a mixture of the two, as in JPEG or IUPAC.

The broader sense of acronym inclusive of terms pronounced as the individual letters (such as "TNT") is sometimes criticized, but it is the term's original meaning[1] and is in common use.[2] Language authorities such as dictionary and style guide editors are not in universal agreement on the naming for such abbreviations: in particular it is a matter of some dispute whether the term acronym can be legitimately applied to abbreviations which are not pronounced "as words"; nor do they agree on the correct use of space, case, and punctuation.