A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The word is a portmanteau of back and acronym.

An acronym, a type of abbreviation, is a word or name consisting of parts of the full name's words. Some authorities add that an acronym must be pronounced as a single word rather than individual letters, so considering NASA an acronym but not USA; the latter they instead call an initialism or alphabetism, for a string of initial letters which are pronounced individually. Acronyms commonly are formed from initials alone, such as NATO, FBI, YMCA, GIF, EMT, and PIN, but sometimes use syllables instead, as in Benelux, NAPOCOR, and TRANSCO. They can also be a mixture, as in radar and MIDAS.