A language which has been generated naturally in a particular area or by an ethnic group such as English, French or Japanese is called a “Natural language”. In contrast, a language which has been made in a shorter period and artificially by an individual or more particular group is called a “Constructed language (Conlang)”.
Almost all human beings in history have spoken and have used natural languages as the native languages or the national languages, and almost all fields of academic studies such as learning languages, literature, linguistics, and formation of national languages are based on only natural languages. Human agencies such as nations, politics, laws, economics, education and cultures are also described and managed by them.
However, mainly in Europe and the United States, there are many speakers, institutes and communities of conlangs regardless of whether they treat conlangs as academics or as hobbies, and conlangs have established reputation as the topic and field of cultural and mental activities by human beings.
The most famous conlangs in practical use nowadays are Esperanto (used as a daily language and an international auxiliary language), computer languages (famous as programming languages and so on), auxiliary languages for people with disorders such as sign languages and Braille, and secret languages in market spaces and stores by wholesalers.
Some conlangers create all parts of each language by themselves, others makes only letters or words. The conlang made up of so many original parts (letters, voices and words) is called “a priori language”, and the one which is partly original is “a posteriori language”. Oddly enough, conlangers do not have to make original grammar in order to let their conlangs get reputation as “a priori”, since “a priori” do not mean the originality of grammar but that of letters and words by the custom of conlangers’ communities nowadays.
Furthermore, in the first place, some think every natural language is a conlang, others assert the conlangs they have been using are natural ones. Therefore, there is no established theory about a classification way of conlangs.
As the present circumstance of conlangs in Japan, there is no academic situation and institute on conlangs and no political establishment on them as official or national languages, but conlangs have a large scale and a great popularity as hobbies when compared to the other nations. Almost all conlangers in Japan tend to enjoy conlangs as hobbies combined with coterie activities and subcultures such as Anime(animations), Manga(comics) and games, and we can find more than 100 conlangs of Japanese origin on the Internet. However, while a large amount of conlangs has been made as hobbies by university students or younger, almost all of them have deserted their conlangs to become adults who earn one's own living and proper reputation. Therefore, there are only a few conlangs which are covered and studied in academic communities.