A constructed language (sometimes called a conlang) is a language whose phonology, grammar, and vocabulary, instead of having developed naturally, are consciously devised or invented as a work of fiction. Constructed languages may also be referred to as artificial languages, planned languages or invented languages and in some cases, fictional languages. Planned languages are languages that have been purposefully designed. They are the result of deliberate controlling intervention, thus of a form of language planning.
There are many possible reasons to create a constructed language, such as to ease human communication (see international auxiliary language and code); to give fiction or an associated constructed setting an added layer of realism; for experimentation in the fields of linguistics, cognitive science, and machine learning; for artistic creation; and for language games. Some people make constructed languages simply because they like doing it.
The expression planned language is sometimes used to indicate international auxiliary languages and other languages designed for actual use in human communication. Some prefer it to the adjective artificial, as this term may be perceived as pejorative. Outside Esperanto culture, the term language planning means the prescriptions given to a natural language to standardize it; in this regard, even a "natural language" may be artificial in some respects, meaning some of its words have been crafted by conscious decision. Prescriptive grammars, which date to ancient times for classical languages such as Latin and Sanskrit, are rule-based codifications of natural languages, such codifications being a middle ground between naïve natural selection and development of language and its explicit construction. The term glossopoeia is also used to mean language construction, particularly construction of artistic languages.
Conlang speakers are rare. For example, the Hungarian census of 2011 found 8,397 speakers of Esperanto, and the census of 2001 found 10 of Romanid, two each of Interlingua and Ido and one each of Idiom Neutral and Mundolinco. The Russian census of 2010 found that there were in Russia about 992 speakers of Esperanto (on place 120), nine of Ido and one of Edo.