Conlang stands for constructed language, in contrast to natlang for "natural language". Other general terms in use for conlangs in the past, but less popular in recent years, include "artificial language" and "model language"; the latter term was popularized by Jeffrey Henning in the mid-1990s, but seems to have fallen out of general use.
There are various types of conlang:
- Engineered languages (engelangs [/ˈendʒlæŋz/]
), further subdivided into philosophical languages, logical languages (loglangs) and experimental languages; devised for the purpose of experimentation in logic, philosophy or linguistics. The term was originated in February 2001 by John Cowan and And Rosta.
- Auxiliary languages (auxlangs) — devised for international communication (also IALs, for International Auxiliary Language, or conIALs, constructed international auxiliary languages, by contrast with Latin or other natlangs which have been used as IALs)
- Artistic languages (artlangs) — devised to create aesthetic pleasure or humorous effect
This classification system grew out of discussions on the CONLANG mailing list in the late 1990s and early 2000s. Ray Brown explains it on his web site in terms of the "Gnoli triangle"; many conlangs are not at the vertices of the triangle (pure engelang, auxlang, or artlang) but somewhere along the lines or in the space in the middle.
Other terms used for describing or classifying conlangs include:
- A posteriori conlangs (from Latin: "posterior", 'later'/'after') are conlangs derived from existing, natural languages. The best known example of an a posteriori conlang is probably Esperanto, which draws mainly from Latin and other, mainly European languages' vocabulary and grammar. A posteriori languages usually have the primary aim to be very easy to learn because they 'feel' natural. This, however, tends to be only true for a certain percentage of the population. Esperanto, for instance, is clearly easier to learn for Italians, Hispanics, Frenchmen or anyone that has studied Latin, than for Germans, Arabs or Asians in general.
- A priori conlangs (from Latin: "prior", 'sooner'/'before') are conlangs that exist within a proper, also constructed language family. They aren't related to any human language. These conlangs tend to have the primary aim to be equally easy to learn for anyone with any native background, which unfortunately usually entails a more abstract, less natural grammar and thus a harder learning difficulty.
- Personal language, hermetic language, or heartlang, a language someone creates for personal use; the latter two terms emphasize that they try to become fluent in their language to use it in expressing their private thoughts in a way that natlangs or other conlangs aren't suitable for. Javant Biarujia's Taneraic is probably the most famous such hermetic language; Paul Burgess's mna Vanantha was recently discussed at length in Sarah L. Higley's Hildegard of Bingen's Unknown Language.
- Romlang, a naturalistic artlang derived from Vulgar Latin or Proto-Romance; usually set in an alternate history where the Roman Empire's linguistic influence was stronger in some area than it was in our own history. Andrew Smith's Brithenig is the granddaddy of romlangs.
- Altlang, a more general term for an alternate-history artlang, especially naturalistic diachronically derived artlangs such as romlangs
- Fauxlang, a conlang with the design criteria of an auxlang but without the political goals of an auxlang ("the same thing we do every night, Pinky... try to take over the world!"). Some fauxlangs are also altlangs, auxlangs created by a fictional serious auxlanger in an alternate history; e.g. Rex May's Texperanto (created by a Zamenhof who immigrated to the Republic of Texas), and Ray Brown's Ελληνικό άνευ Κλίσι, a Greek-empire-timeline version of Peano's Latine Sine Fleksione
- Taxonomic languages are usually engelangs, specifically philosophical languages, where the sequence of phonemes in a word specifies the position of the concept it represents in a taxonomic hierarchy; examples are Ro and John Wilkins' Real Character.
- Exolang, a language spoken by fictional nonhuman aliens, especially if it also violates human language universals. Quenya is spoken by fictional nonhumans, but probably wouldn't be called an exolang because it looks like a typical human language. Admired exolangs include Sylvia Sotomayor's Kēlēn and Jeffrey Henning's Fith. This term seems to be most used on the Conlang Relay list; elsewhere "alien language" might be more common.
- Euroclone, a term used primarily on the AUXLANG list but also elsewhere, is used generally to refer to auxlangs that more or less resemble Western European models. Some use the term more restrictively for a narrow set of auxlangs like Interlingua; some a bit more broadly to include more schematic European-based auxlangs like Esperanto and Ido. The term is pejorative as used by some speakers, particularly those who think an ideal auxlang should be based on worldwide rather than primarily or exclusively European sources.
- Worldlang, a term primarily used on the AUXLANG list; sometimes to mean an auxlang intended for global use in contrast to one intended for regional (e.g. Europe only) use, more recently used to refer to auxlangs that take their vocabulary from a variety of natlangs of different language families, not just Western European languages. Some users of the term seem to emphasize globally accessible lowest-common denominator phonology and grammar, as well (e.g., CV syllables with a small phoneme inventory; few or no mandatory inflectional categories).
- Hagioglossa or ritlang, terms coined on the CONLANG list but rarely used as yet, a conlang devised for religious or ritual purposes (prayer, meditation, worship, etc.)
- Planlang, occasionally proposed as a synonym of "engelang" but scarcely used in that sense, and also (slightly more often but not very often) used as an abbreviation of "planned language", a common term for auxlangs
- Lablang, occasionally proposed as a synonym of "engelang" but rarely used
- Sketchlang, a conlang whose grammar or vocabulary or both is very incomplete; perhaps implying that the creator has no intention of fully developing it
These terms are used more descriptively than classificationally:
- Relex, a term of criticism saying that someone has naïvely or unreflectively imitated their native language too closely in creating a conlang. Many conlangers' first attempts at conlanging are relexes of their native language on one level or another. Also occasionally called "codes" or "cipherlangs".
- Kitchen sink conlang, a term of criticism saying that someone has thrown in too many features in their conlang without considering how they work together or what the overall ethos of the conlang should be. Sai Emrys doesn't use the term in his Conlang Evaluation essay, but he probably has this kind of thing in mind in saying "Somebody’s been learning new things in Linguistics class again..." Many conlangers' second attempts at conlanging are kitchen sink collections of all the neat features they've been reading about lately and the spiffy phonemes they've just learned to pronounce.
- Maggelity', a term used mostly on the CONLANG mailing list to describe the quality of conlangs with extreme degrees of irregularity even beyond what's found in natlangs; from Christophe Grandsire's conlang Maggel and its baroque orthography and grammar. Also adjective forms maggelic, maggelitous, maggelitinous.
- Etabnannery, adj. etabnanneric or etabnannimous: a quality of languages with extremely complex but regular orthography, usually due to retention of archaically phonemic spelling, or spelling that fails to reflect sandhi and other phonological processes.
- ANADEW: Another Natlang Already Did it Even Worse. The phenomenon of discovering that a weird, supposedly original feature in your conlang already exists in some natural language. Also, "anadewism".
There are some grammatical or typological terms that are used only with respect to conlangs, or have a different sense with respect to conlangs although they originated in standard linguistics:
- Trigger languages have an unusual type of morphosyntactic alignment some of which are found only in conlangs. The term, and the way the conlangs work, was apparently inspired by attempts to understand the applicativization systems of Austronesian languages like Tagalog. "Austronesian alignment" refers to this this specific alignment, but a trigger system is one in which the verb somehow indicates the grammatical case of one or more nouns. 
- Oligosynthetic languages, where all words are built from a fairly small set of root morphemes, apparently don't exist in the wild but there are a few conlangs of that nature; similarly oligoisolating languages with a restricted set of root words that don't compound but express more complex meanings through phrases, e.g. Toki Pona or to a lesser extent Basic English.
- Correlative is a catch-all term used in Esperanto grammar, and sometimes in describing conlangs whose design was influenced by Esperanto, to refer to demonstratives, interrogative and relative pronouns and adverbs, and (especially if they are morphologically related to the aforementioned particles in a given language, as they are in Esperanto) words such as "someone", "nowhere", "anyhow", etc.
- Self-segregating morphology is a quality some auxlangs and many engelangs have whereby one can always tell at a glance where one morpheme or word leaves off and another begins.
- Verb-drop, a term coined by analogy with "pro-drop", a term for conlangs where the verb can be omitted when it's obvious from the cases or adpositions applied to the nouns in a sentence: "Sam ate oranges and Carly pears."