a language that is deliberately created for a specific purpose

a language that has been deliberately designed by one person or a small group of people over a relatively short period of time

an idiom that has not developed in a speech community like a natural tongue but has been constructed by human agents from various materials, such as devised signs, elements or modified elements taken from existing natural languages, and invented forms

a simple model of a natural language

A language that is designed for a special purpose; it can be a formal language, like FOL, or more akin to natural language, like Esperanto.