Acronym

==Orthographic styling==
===Punctuation===
====Showing the ellipsis of letters====
In English, abbreviations have previously been marked by a wide variety of [[English punctuation|punctuation]]. Obsolete forms include using an [[overbar]] or [[colon (punctuation)|colon]] to show the [[ellipsis]] of letters following the initial part. The [[forward slash]] is still common in many dialects for some fixed expressions{{mdash}}such as ''w/'' for "with" or ''A/C'' for "[[air conditioning]]"{{mdash}}while only infrequently being used to abbreviate new terms. The [[apostrophe]] is common for [[Contraction (grammar)#English|grammatical contractions]] (e.g. ''don't'', ''[[y'all]]'', and ''[[ain't]]'') and for contractions marking unusual pronunciations (e.g. ''a'ight'', ''cap'n'', and ''fo'c'sle'' for "all right", "captain", and "forecastle"). By the early twentieth century, it was standard to use a [[full stop|full stop/period/point]], especially in the cases of initialisms and acronyms. Previously, especially for [[Latin abbreviations]], this was done with a full space between every full word (e.g. {{lang|la|A. D.}}, {{lang|la|i. e.}}, and {{lang|la|e. g.}} for "[[Anno Domini]]", "[[id est]]", and "[[exempli gratia]]"). This even included punctuation after both [[Roman numerals|Roman]] and [[Arabic numerals]] to indicate their use in place of the full names of each number (e.g. ''LII.'' or ''52.'' in place of "fifty-two" and "1/4." or "1./4." to indicate "one-fourth"). Both conventions have fallen out of common use in all dialects of English, except in places where an Arabic [[decimal number|decimal]] includes a medial [[decimal point]].

Particularly in [[British English|British]] and [[Commonwealth English]], all such punctuation marking acronyms and other capitalized abbreviations is now uncommon and considered either unnecessary or incorrect. The presence of all-capital letters is now thought sufficient to indicate the nature of the ''[[United Kingdom|UK]]'', the ''[[European Union|EU]]'', and the ''[[United Nations|UN]]''. Forms such as ''the U.S.A.'' for "the [[United States of America]]" are now considered to indicate [[American English|American]] or [[North American English]]. Even within those dialects, such punctuation is becoming increasingly uncommon.<ref>[[Oxford English Dictionary]]: ''initialism''. "Globe & Mail (Toronto) 22 May 10/4 Americanization has also largely done away with periods in acronyms and initialisms."</ref>

=====Ellipsis-is-understood style=====
Some [[style guide]]s, such as that of the [[BBC]], no longer require punctuation to show [[ellipsis]]; some even proscribe it. [[Larry Trask]], American author of ''The [[Penguin Books|Penguin]] Guide to Punctuation'', states categorically that, in [[British English]], "this tiresome and unnecessary practice is now obsolete."<ref>{{cite web |url= http://www.informatics.susx.ac.uk/doc/punctuation/node28.html |title=Abbreviations |publisher=Informatics.Susx.ac.uk |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20070410113359/http://www.informatics.susx.ac.uk/doc/punctuation/node28.html |archive-date=April 10, 2007 }}</ref>

=====Pronunciation-dependent style and periods=====
Nevertheless, some influential [[style guide]]s, many of them [[American English|American]], still require periods in certain instances. For example, ''[[The New York Times Manual of Style and Usage]]'' recommends following each segment with a period when the letters are pronounced individually, as in "[[KGB|K.G.B.]]", but not when pronounced as a word, as in "[[NATO]]".<ref name = "NY Times">{{Cite news |url= https://www.nytimes.com/2004/02/07/opinion/secret-obsessions-at-the-top.html |access-date=October 10, 2015 |title=Secret Obsessions at the Top |first=Nicholas D. |last=Kristoff |work=[[The New York Times]] |date=February 7, 2004 |archive-url= https://web.archive.org/web/20150528024321/http://www.nytimes.com/2004/02/07/opinion/secret-obsessions-at-the-top.html |archive-date=May 28, 2015 |url-status=live}}</ref> The logic of this style is that the pronunciation is reflected graphically by the punctuation scheme.

=====Other conventions=====
When a multiple-letter abbreviation is formed from a single word, periods are in general not used, although they may be common in informal usage. "TV", for example, may stand for a ''single'' word ("television" or "transvestite", for instance), and is in general spelled without punctuation (except in the plural). Although "PS" stands for the single English word "[[postscript]]" or the Latin ''postscriptum'', it is often spelled with periods ("P.S.") as if parsed as Latin ''post scriptum'' instead.

The [[slash (punctuation)|slash]] ('/', or ''solidus'') is sometimes used to separate the letters in an acronym, as in "N/A" ("not applicable, not available") and "c/o" ("care of").

Inconveniently long words used frequently in related contexts can be represented according to their letter count as a [[numeronym]]. For example, "i18n" abbreviates "[[internationalization]]", a computer-science term for adapting software for worldwide use. The "18" represents the 18 letters that come between the first and the last in "internationalization". "Localization" can be abbreviated "l10n", "[[multilingualization]]" "m17n", and "[[accessibility]]" "a11y". In addition to the use of a specific number replacing that many letters, the more general "x" can be used to replace an unspecified number of letters. Examples include "Crxn" for "crystallization" and the series familiar to physicians for [[medical history|history]], [[medical diagnosis|diagnosis]], and [[therapy|treatment]] ("hx", "dx", "tx"). Terms relating to a command structure may also sometimes use this formatting, for example gold, silver, and bronze levels of command in UK policing being referred to as Gx, Sx, and Bx.

====Representing plurals and possessives====
There is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, [[Kate L. Turabian]]'s ''[[A Manual for Writers of Research Papers, Theses, and Dissertations]]'', writing about style in academic writings,<ref name="Chicago">{{cite book |last1=Turabian |first1=Kate L. |author1-link=Kate L. Turabian |last2=Booth |first2=Wayne C. |last3=Colomb |first3=Gregory G. |last4=Williams |first4=Joseph M. |title=[[A Manual for Writers of Research Papers, Theses, and Dissertations]] |edition=7th |date=2007 |at=§&nbsp;20.1.2 |publisher=[[University of Chicago Press]] |isbn=978-0-226-82337-9}}</ref> allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" but "Ph.D.'s". The style guides of the [[Modern Language Association]]<ref name="MLA">{{cite book |publisher=[[Modern Language Association]] |title=[[MLA Handbook]] for Writers of Research Papers |edition=7th |date=2009 |at=§&nbsp;3.2.7.g}}</ref> and [[American Psychological Association]]<ref name="APA">{{cite book |title=Publication Manual of the American Psychological Association |edition=5th |date=2001 |at=§&nbsp;3.28 |publisher=[[American Psychological Association]]}}</ref><ref name=autogenerated1>{{cite book |title=[[Publication Manual of the American Psychological Association]] |edition=6th |date=2010 |at=§&nbsp;4.29 |publisher=[[American Psychological Association]]}}</ref> prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas ''[[The New York Times Manual of Style and Usage]]'' requires an apostrophe when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's").<ref>{{cite book |last1=Siegal |first1=Allan M. |author1-link=Allan M. Siegal |last2=Connolly |first2=William G. |author2-link=William G. Connolly |title=[[The New York Times Manual of Style and Usage]] |page=[https://www.google.com/books/edition/The_New_York_Times_Manual_of_Style_and_U/CnwIVkAQgFwC?hl=en&gbpv=1&pg=PA263 263] |via=Google Books |publisher=Three Rivers Press |date=1999}}</ref>

Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, "the C.D.'s' labels" (the labels of the compact discs). In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is "S", as in "SOS's" (although abbreviations ending with S can also take "-es", e.g. "SOSes"), or when pluralizing an abbreviation that has periods.<ref>{{cite web |url= http://www.writersblock.ca/tips/monthtip/tipmar96.htm |title=Writer's Block&nbsp;– Writing Tips&nbsp;– Plural and Possessive Abbreviations |publisher=WritersBlock.ca |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20100726124408/http://www.writersblock.ca/tips/monthtip/tipmar96.htm |archive-date=July 26, 2010}}</ref><ref>{{cite web |url= http://www.editfast.com/english/grammar/apostrophes/apostrophe_plurals.htm |title=EditFast Grammar Resource: Apostrophes: Forming Plurals |publisher=Editfast.com |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20101027001351/http://editfast.com/english/grammar/apostrophes/apostrophe_plurals.htm |archive-date=October 27, 2010 }}</ref>

A particularly rich source of options arises when the plural of an acronym would normally be indicated in a word other than the final word if spelled out in full. A classic example is "Member of Parliament", which in plural is "Members of Parliament". It is possible then to abbreviate this as "M's P", which was fairly common in mid-twentieth-century Australian news writing<ref>{{cite web |url= https://trove.nla.gov.au/work/26924909 |title=Libraries Australia&nbsp;– T.H. McWilliam, Charles Kingsford Smith, Prime Minister of New Zealand Joseph Coates, Charles Ulm and H.A. Litchfield in front row with Members of Parliament on steps of Parliament House, Wellington, New Zealand, September 1928 |at=Notes |work=NLA.gov.au |publisher=[[National Library of Australia]] |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20080622132412/http://nla.gov.au/anbd.bib-an41354070 |archive-date=June 22, 2008 |url-status= live}}</ref><ref>{{cite web |first=Robin |last=Hyde |url= https://nzetc.victoria.ac.nz/tm/scholarly/tei-HydJour-t1-body-d3.html |title=Chapter III.&nbsp;— The House is in Session |publisher=NZETC |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20110430012333/https://nzetc.victoria.ac.nz/tm/scholarly/tei-HydJour-t1-body-d3.html |archive-date=April 30, 2011 |url-status=live}}</ref> (or similar<ref>{{cite web |url= http://www.middlemiss.org/lit/authors/denniscj/backblockother/underpartyplan.html |title=Under the party plan |first=C. J. |last=Dennis |author-link=C. J. Dennis |work=[[The Bulletin (Australian periodical)|The Bulletin]] |date=January 18, 1912 |page=43 |via=Middlemiss.org |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20100822175445/http://www.middlemiss.org/lit/authors/denniscj/backblockother/underpartyplan.html |archive-date=August 22, 2010 |url-status=live}}</ref>), and used by former Australian Prime Minister [[Ben Chifley]].<ref>{{cite news |url= https://trove.nla.gov.au/newspaper/page/5605107 |via=Trove.NLA.gov.au |title=M's.P. Suffer Loss and Insecurity |date=December 2, 1948 |work=[[Townsville Bulletin|Townsville Daily Bulletin]] |page=1}}</ref><ref>{{cite news |url= https://trove.nla.gov.au/newspaper/article/27755397 |date=October 14, 1948 |title=Prime Minister Asserts M's.P. Have No Immunity from 'Official Approaches' |work=[[The Mercury (Hobart)|The Mercury]] |page=2 |via=Trove.NLA.gov.au}}</ref><ref>{{cite web |url= http://www.electricscotland.com/history/australia/melbourne11.htm |title=The Royal Caledonian Society of Melbourne |via=ElectricScotland.com |access-date=January 21, 2013 |archive-url= https://web.archive.org/web/20120715091217/http://www.electricscotland.com/history/australia/melbourne11.htm |archive-date=July 15, 2012 |url-status=live}}</ref> This usage is less common than forms with "s" at the end, such as "MPs", and may appear dated or pedantic. In common usage, therefore, "weapons of mass destruction" becomes "WMDs", "prisoners of war" becomes "POWs", and "runs batted in" becomes "RBIs".<ref>{{cite book |last=Garner |first=Bryan |author-link=Bryan Garner |title=[[Garner's Modern American Usage]] |date=August 27, 2009 |publisher=Oxford University Press |location=Oxford / New York |isbn=978-0-19-538275-4 |page=638}}</ref>

The argument that acronyms should have no different plural form (for example, "If ''D'' can stand for ''disc'', it can also stand for ''discs''") is in general disregarded because of the practicality in distinguishing singulars and plurals. This is not the case, however, when the abbreviation is understood to describe a plural noun already: For example, "U.S." is short for "United States", but not "United State". In this case, the options for making a possessive form of an abbreviation that is already in its plural form without a final "s" may seem awkward: for example, "U.S.", "U.S.'s", etc. In such instances, possessive abbreviations are often forgone in favor of simple [[adjective|attributive]] usage (for example, "the U.S. economy") or expanding the abbreviation to its full form and ''then'' making the possessive (for example, "the United States' economy"). On the other hand, in speech, the pronunciation "United States's" is sometimes used.

Abbreviations that come from single, rather than multiple, words – such as "TV" ("television") – are usually pluralized without apostrophes ("two TVs"); most writers feel that the apostrophe should be reserved for the possessive ("the TV's antenna").

{{anchor|pp|PP|pP|Pp|page|pages}} In some languages, the convention of doubling the letters in the acronym is used to indicate plural words: for example, the Spanish {{lang|es|EE.UU.}}, for {{lang|es|Estados Unidos}} ('United States'). This old convention is still followed for a limited number of English abbreviations, such as ''SS.'' for ''Saints'', ''pp.'' for the Latin plural of 'pages', {{lang|la|paginae}}, or ''mss.'' for ''manuscripts''.

{{further|English possessive}}

===Case===
====All-caps style====
The most common [[capitalization]] scheme seen with acronyms is all-uppercase ([[all caps]]). [[Small caps]] are sometimes used to make the run of capital letters seem less jarring to the reader. For example, the style of some American publications, including the ''[[Atlantic Monthly]]'' and ''[[USA Today]]'', is to use small caps for acronyms longer than three letters;{{Citation needed|date=August 2007}} thus "U.S." and "[[Franklin D. Roosevelt|FDR]]" in normal caps, but "{{smallcaps|nato}}" in small caps. The acronyms "[[Anno Domini|AD]]" and "[[Before Christ|BC]]" are often smallcapped as well, as in: "From {{nowrap|4004 {{smallcaps|bc}} to {{smallcaps|ad}} 525}}".

====Normal case and anacronyms<span class="anchor" id="Anacronym"></span>====
Where an acronym has linguistically taken on an identity as regular word, the acronym may use normal case rules, e.g. it would appear generally in lower case, but with an initial capital when starting a sentence or when in a title. Once knowledge of the words underlying such an acronym has faded from common recall, the acronym may be termed an '''anacronym'''.<ref>{{ShorterOxfordEnglishDictionary}}</ref> Examples of anacronyms are the words "[[scuba set|scuba]]", "[[radar]]", and "[[laser]]".  The word "an''acro''nym" should not be confused with the word "[[Misnomer#Anachronym|an''achro''nym]]", which is a type of misnomer.

====Mixed-case variant====
Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, "pre-WWII politics", "post-NATO world", "[[DNase]]". In some cases a derived acronym may also be expressed in mixed case. For example, "[[messenger RNA]]" and "[[transfer RNA]]" become "mRNA" and "tRNA".

====Pronunciation-dependent style and case====
Some publications choose to capitalize only the first letter of acronyms, reserving all-caps styling for initialisms, writing the pronounced acronyms "Nato" and "Aids" in mixed case, but the initialisms "USA" and "FBI" in all caps. For example, this is the style used in ''[[The Guardian]]'',<ref>{{Cite news |url= https://www.theguardian.com/styleguide |title=Styleguide |work=[[The Guardian]] |location=London |date=December 19, 2008 |quote=Use all capitals if an abbreviation is pronounced as the individual letters (an initialism): BBC, CEO, US, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, Unicef, unless it can be considered to have entered the language as an everyday word, such as [[awol]], [[laser]] and, more recently, [[asbo]], [[pin number]] and [[sim card]]. Note that [[pdf]] and [[public limited company|plc]] are lowercase.}}</ref> and ''[[BBC News]]'' typically edits to this style (though its official style guide, dating from 2003, still recommends all-caps<ref>{{Cite news|url= http://www.bbctraining.com/pdfs/newsstyleguide.pdf |title=BBC News Style Guide |work=BBCTraining.com |publisher=[[BBC]] |archive-url= https://web.archive.org/web/20110707214856/http://www.bbctraining.com/pdfs/newsStyleGuide.pdf |archive-date=July 7, 2011}}</ref>). The logic of this style is that the pronunciation is reflected graphically by the capitalization scheme. However, it conflicts with conventional English usage of first-letter upper-casing as a marker of proper names in many cases; e.g. ''AIDS'' stands for ''acquired immuno-deficiency syndrome'' which is not a proper name, while ''Aids'' is in the style of one.

Some style manuals also base the letters' [[Letter case|case]] on their number. ''[[The New York Times]]'', for example, keeps "NATO" in all capitals (while several guides in the British press may render it "Nato"), but uses lower case in "[[United Nations Children's Fund|Unicef]]" (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals").

===Numerals and constituent words===
While abbreviations typically exclude the initials of short [[function word]]s (such as "and", "or", "of", or "to"), this is not always the case. Sometimes function words are included to make a pronounceable acronym, such as CORE ([[Congress of Racial Equality]]). Sometimes the letters representing these words are written in lower case, such as in the cases of "TfL" ("[[Transport for London]]") and ''LotR'' (''[[The Lord of the Rings]]''); this usually occurs when the acronym represents a multi-word proper noun.

Numbers (both [[cardinal number|cardinal]] and [[ordinal number|ordinal]]) in names are often represented by [[numerical digit|digit]]s rather than initial letters, as in "4GL" ("[[fourth generation language]]") or "G77" ("[[Group of 77]]"). Large numbers may use [[SI prefix#Use outside SI|metric prefixes]], as with "[[2000|Y2K]]" for "Year 2000". Exceptions using initials for numbers include "[[three letter acronym|TLA]]" ("three-letter acronym/abbreviation") and "GoF" ("[[Gang of Four (software)|Gang of Four]]"). Abbreviations using numbers for other purposes include repetitions, such as "[[A2DP]]" ("Advanced Audio Distribution Profile"), "[[W3C]]" ("World Wide Web Consortium"), and ''[[WVOX#Notable Past Programming|T3]]'' (''Trends, Tips & Tools for Everyday Living''); pronunciation, such as "[[Business-to-business|B2B]]" ("business to business"); and [[numeronym]]s, such as "i18n" ("internationalization"; "18" represents the 18 letters between the initial "i" and the final "n").

===Casing of expansions===
Authors of [[expository writing]] will sometimes capitalize or otherwise distinctively format the initials of the expansion for [[pedagogical]] emphasis (for example, writing: "the onset of Congestive Heart Failure (CHF)" or "the onset of '''c'''ongestive '''h'''eart '''f'''ailure (CHF)"). Capitalization like this, however, conflicts with the convention of English orthography, which generally reserves capitals in the middle of sentences for proper nouns; when following the [[AMA Manual of Style]], this would instead be rendered as "the onset of congestive heart failure (CHF)".<ref name="AMA10p442">{{Citation |editor-last=Iverson |editor-first=Cheryl |display-editors=etal |title=AMA Manual of Style |edition=10th |publisher=[[Oxford University Press]] |location=Oxford, Oxfordshire |year=2007 |isbn=978-0-19-517633-9 |page=[https://archive.org/details/amamanualofstyle0000unse/page/442 442]}}</ref>