Artlang Overview

"Conlang" is short for "constructed language," and refers to a languages deliberately constructed by a small group of people, as opposed to a "natlang," or "natural language." There are three basic classifications of conlangs:

Auxlangs: Auxiliary languages are devised with the intent of creating a universal language. Esperanto is the most famous example.
Engelangs: Engineered languages are devised to experiment with the limits of language or communication, or to create a language with specific contraints or features. Lojban, for instance, is a logical language meant to have as few ambiguities as possible. Toki Pona is meant to test lexical minimalism by having only 120 root words.
Artlangs: Artistic languages are devised either for the aesthetic pleasure of the creator (such as for a personal diary) or to create a language for fictional purposes. J. R. R. Tolkien created several artlangs for his Middle Earth books. Klingon is another famous artlang.

Artlangs, in turn, can be identified according to the creator's intent:

Altlangs: Alternate History Artlangs tend to be based on natlangs, with changes that reflect some difference in the timeline. For instance, in A Clockwork Orange, Anthony Burgess imagines how English might have changed in the future, and writes the entire text of the novel in that language; however, in this case, the main difference was in the words used, while grammar and sounds stayed the same. A more robust altlang might start with the premise the Rome didn't collapse, and build a modern form of Latin.
Exolangs: Extraterrestrial Artlangs are designed to throw out natlangs and start as fresh as possible. If the speakers of the language have different vocal structures than humans, sounds may be added or dropped. Word choice and grammar aren't constrained by human rules.

These two classifications reflect ends of a scale rather than immutably defined taxonomic buckets. For instance, an author might be devising a language for an as yet unidentified tribe from the Amazon, in which case (s)he might study other languages of the region for a touchstone but would have greater liberty for creating some new linguistic patterns. Somebody writing about a planet similar to Earth may choose to make the inhabitants similar to humans or completely different, and that choice would be reflected in the artlang.

My current primary interest is in artlangs, although I've studied Esperanto in the past.