Abbreviation is the general term used to describe any shortened word. Contractions and acronyms are types of abbreviation. A contraction is a word that has been squeezed in the middle, so to speak, but has retained one or more of its opening and closing letters, as with Mr. for Mister and canâ€™t for cannot. An acronym is a word formed from the initial letter or letters of a group of words, as with radar for radio detecting and ranging, and NATO for North Atlantic Treaty Organization. Abbreviations that are not pronounced as words (IBM, ABC, NFL) are not acronyms; they are just abbreviations.