An acronym (Greek ακρον, akron, "tip" + ονυμα, onyma, "name") is an abbreviation formed from the initial letters of words. Depending on how many of the constituent words begin with vowels and the phonotactics of the language an acronym exists in, acronyms can be pronounced as a word, as a series of the names of the letters, or some combination of the two. Sometimes acronyms have idiosyncratic pronunciations, like NAACP, which is pronounced "N double A C P".
Acronyms often occur in jargon or as names of organizations because they often serve as abbreviations of long terms that are frequently referenced, so a shortened form is desirable. Cynics have quipped that acronyms are used to obfuscate.
Traditionally, abbreviations use a period (full stop) to mark the part that was deleted. In the case of acronyms, each letter is its own abbreviation, and in theory should get its own period. This usage is becoming less common as the presence of all capital letters is sufficient to indicate the word is an abbreviation; nevertheless some influential usage guides still insist on the many-periods treatment, such as the one used by the New York Times, but others—most notably, at the BBC—no longer require this. (See the Wikipedia article: abbreviation)Some acronyms undergo assimilation into ordinary words: often they are written in lower case, and eventually it is widely forgotten that the word was derived from the initials of others: scuba and laser, for instance. The term anacronym has been coined as a combination of the words "anachronism" and "acronym" to describe acronyms whose original meaning is forgotten.
There is debate over whether the word acronym can be applied to any set of initials. Some people insist an acronym is only a set of initials which is pronounceable as a word. Some dictionary definitions can be interpreted to support this view. Under this view, sets of initials like "BBC" and "IBM" are initialisms and not acronyms. On the other hand, under the restrictive definition of "acronym" there is no English word to describe all strings of initials that are used in place of the full words. Many people use the word acronym for all such sets of initials regardless of whether they are pronounced as a word or as the names of the letters in sequence.
Sometimes non-initial letters, and the initials of short function words (such as "and", "or", "of", or "to") are included in the acronym to make it pronounceable, in contradiction to the normal rule for abbreviation. Additionally, abbreviations like "Interpol" and "Gestapo" that consist mostly of non-initial letters of constituent words are often called acronyms, although some people class them instead portmanteaus.
The traditional style of pluralizing single letters with "'s" ("there are two Q's in that word") was naturally extended to acronyms when they were commonly written with periods, and is still preferred by some people, especially when the acronym is pronounced as separate letters. However, today it is more usual to inflect them like ordinary words; thus the usual plural of "CD" is "CDs", with "CD's" being reserved for the possessive.
The world's longest acronym, according to the Guinness Book of World Records is NIIOMTPLABOPARMBETZHELBETRABSBOMONIMONKONOTDTEKHSTROMONT. The 56-letter acronym (54 in Cyrillic) is from the Concise Dictionary of Soviet Terminology and means "The laboratory for shuttering, reinforcement, concrete and ferroconcrete operations for composite-monolithic and monolithic constructions of the Department of the Technology of Building-assembly operations of the Scientific Research Institute of the Organization for building mechanization and technical aid of the Academy of Building and Architecture of the USSR". The longest acronym according to the 1965 edition of the Acronyms, Initialisms and Abbreviations Dictionary is ADCOMSUBORDCOMPHIBSPAC, a United States Navy term that stands for "Administrative Command, Amphibious Forces, Pacific Fleet Subordinate Command".
During the 1960s trend for action-adventure spy thrillers, it was a common practice for fictional spy organizations or their nemesis to employ names that were acronyms. Sometimes these acronyms made sense but most of the time, they were words incongrously crammed together for the mere purpose of obtaining a catchy acronym, traditionally a heroic sounding one for the good guys and an appropriately menacing one for the bad guys. This has become one of the most commonly parodied cliches of the spy thriller genre. Some of the most popular were: