Acronym

===Macronyms/nested acronyms===
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A '''macronym''', or '''nested acronym''', is an acronym in which one or more letters stand for acronyms (or abbreviations) themselves. The word "macronym" is a [[portmanteau]] of "[[wikt:macro-|macro-]]" and "acronym".

Some examples of macronyms are:<!-- with citations in each individual article's references -->
* [[XMLHttpRequest|XHR]] stands for "XML HTTP Request", in which "[[XML]]" is "Extensible Markup Language", and [[HTTP]] stands for "HyperText Transfer Protocol"
* [[IBM Power microprocessors|POWER]] stands for "Performance Optimization With Enhanced RISC", in which "[[RISC]]" stands for "reduced instruction set computer"
* [[VHDL]] stands for "VHSIC Hardware Description Language", in which "[[VHSIC]]" stands for "Very High Speed Integrated Circuit"
* [[XSD]] stands for "XML Schema Definition", in which "[[XML]]" stands for "Extensible Markup Language"
* [[AOL Instant Messenger|AIM]] stands for "AOL Instant Messenger", in which "[[AOL]]" originally stood for "America Online"
* [[Houston Automatic Spooling Priority|HASP]] stood for "Houston Automatic Spooling Priority", but "[[spooling]]" itself was an acronym: "simultaneous peripheral operations on-line"
* [[VORTAC]] stands for "VOR+TACAN", in which "VOR" is "[[VHF omnidirectional range]]" (where VHF = very high frequency radio) and "TAC" is short for [[TACAN]], which stands for "tactical air navigation"
* [[Global Information Assurance Certification]] has a number of nested acronyms for its certifications, e.g. "GSEC" is an acronym for "GIAC Security Essentials"
* [[REM behaviour disorder|RBD]] stands for "REM Behavior Disorder", in which "[[Rapid eye movement sleep|REM]]" stands for "rapid eye movement"

Some macronyms can be multiply nested: the second-order acronym points to another one further down a hierarchy. In an informal competition run by the magazine ''[[New Scientist]]'', a fully documented specimen was discovered that may be the most deeply nested of all: RARS is the "Regional ATOVS Retransmission Service"; ATOVS is "Advanced TOVS"; TOVS is "[[TIROS]] operational vertical sounder"; and TIROS is "Television infrared observational satellite".<ref>{{cite web|url= https://www.newscientist.com/article/mg20727681.100-very-deep-multiply-nested-acronyms.html |title=Very deep multiply nested acronyms |work=[[New Scientist]] |date=July 7, 2010 |access-date=September 16, 2010 |archive-url= https://web.archive.org/web/20100914033751/http://www.newscientist.com/article/mg20727681.100-very-deep-multiply-nested-acronyms.html |archive-date=September 14, 2010 |url-status=live}}</ref> Fully expanded, "RARS" might thus become "Regional Advanced Television Infrared Observational Satellite Operational Vertical Sounder Retransmission Service", which would produce the much more unwieldy acronym "RATIOSOVSRS".

Another example is [[VHDL-VITAL|VITAL]], which expands to "[[VHDL]] Initiative Towards [[ASIC]] Libraries" (a total of 15 words when fully expanded).

However, to say that "RARS" stands directly for that string of words, or can be interchanged with it in [[syntax]] (in the same way that "CHF" can be usefully interchanged with "congestive heart failure"), is a [[Linguistic prescription|prescriptive]] misapprehension rather than a linguistically accurate description; the true nature of such a term is closer to [[#All-caps style|anacronymic]] than to being interchangeable like simpler acronyms are. The latter are fully reducible in an attempt to "spell everything out and avoid all abbreviations", but the former are irreducible in that respect; they can be [[Gloss (annotation)|annotated]] with parenthetical explanations, but they cannot be eliminated from speech or writing in any useful or practical way. Just as the words ''laser'' and ''radar'' function as words in [[syntax]] and [[cognition]] without a need to focus on their acronymic origins, terms such as "RARS" and "[[CHA2DS2–VASc score]]" are irreducible in [[natural language]]; if they are purged, the form of language that is left may conform to some imposed rule, but it cannot be described as remaining natural. Similarly, [[protein]] and [[gene]] nomenclature, [[Gene nomenclature#Symbol and name|which uses symbols extensively]], includes such terms as the name of the [[NACHT domain|NACHT protein domain]], which reflects the symbols of some proteins that contain the domain – NAIP (NLR family apoptosis [[inhibitor protein]]), C2TA (major histocompatibility complex class II transcription activator), HET-E (incompatibility locus protein from ''Podospora anserine''), and TP1 (telomerase-associated protein) – but is not syntactically reducible to them. The name is thus itself more symbol than acronym, and its expansion cannot replace it while preserving its function in natural syntax as a [[name]] within a [[clause]] clearly [[Parsing|parsable]] by human readers or listeners.

====Recursive acronyms====
{{Main|Recursive acronym}}
A special type of macronym, the [[recursive acronym]], has letters whose expansion refers back to the macronym itself. One of the earliest examples appears in ''[[The Hacker's Dictionary]]'' as [[Mung (computer term)|MUNG]], which stands for "MUNG Until No Good".

Some examples of recursive acronyms are:
* [[GNU]] stands for "GNU's Not Unix!"
* [[LAME]] stands for "LAME Ain't an MP3 Encoder"
* [[PHP]] stands for "PHP: Hypertext Preprocessor"
* [[Wine (software)|WINE]] stands for "WINE Is Not an Emulator"
* [[GNU Hurd|HURD]] stands for "HIRD of Unix-replacing daemons", where HIRD itself stands for "HURD of interfaces representing depth" (a "mutually recursive" acronym)