constructed language

Short definition from Wiktionary

Noun

1. 1
   Any language—whether a human language, a programming language, or markup language—that is not a natural language.
2. 2
   A human language that has been consciously devised by an individual or a group, as opposed to having naturally evolved as part of a culture like a natural language.
3. 3
   Any language used by people, as opposed to less civilized means of communication, such as the socialization between animals.