A backronym is a reverse acronym.
That is, an expression that has been formed from the letters of an existing word or name. The word backronym is a blend of “backward” and “acronym”. It is a constructed phrase which purports to be the source of a word that is an acronym. An acronym, of course, is derived from the initial letters of the words of a phrase. A backronym is an acronym deliberately formed from a phrase whose initial letters spell out a particular word or words, either to create a memorable name or a fanciful explanation of the words origin.”
The difference between an acronym and a backronym is timing. What came first, the phrase or the words.
SCUBA is a true acronym evolved from “Self-Contained Underwater Breathing Apparatus”. For example, radar comes from “radio detection and ranging”. Radar comes from “radio detection and ranging.” GOLF, notwithstanding its etymological myth, does not stand for “gentleman only, ladies forbidden”. That is a backronym.
SARS is a true acronym: Severe Acute Respiratory Syndrome.
Probably, the most well-known medical backronym is one familiar to medical professionals and parents of newborns alike – the Apgar score.
It is an example of a backronym as a mnemonic. An Apgar score is used to assess the health of newborn babies. The system was devised by and named after Virginia Apgar, an United States anaesthesiologist who developed the test in 1952 to evaluate the effects of obstretic anaesthetia on neonates. Apparently, ten years after the initial publication, the backronym APGAR (a mnemonic learning aide: Appearance, Pulse, Grimace, Activity And Respiration) was coined in the United States.
It is suggested that many medical acronyms are probably backronyms, because the names are often chosen to fit the letters of a word rather than becoming a word after abbreviation.
See, for example, the less inspirational and exciting, CHICAGO – Carotid intima-media tHICkness in Atherosclerosis using pioglitazone; FLAIR – magnetic resonance imaging technique fluid-attenuated inversion recovery; and PRES – posterior reversible encephalopathy syndrome.
Backronyms are one way of forming medical terms along with, among others, acronyms, eponyms, toponyms and mythonyms. What medical backronyms can you think of?
 “Backronym – definition of backronym in English by Oxford Dictionaries – Oxford Dictionaries – English
 The Virginia Apgar papers – “Obstretics and Anaesthetia and a scorecard for newborns, 1949 – 1958” USA National Library of Medicine NIH retrieved 2008-11-18
 Jeffrey Aronson When I use a word . . . Backronyms” in thebmjopinion https://blogs.bmj.com/bmj/2015/08/14/jeffrey-aronson-when-i-use-a-word-backronyms/