Esoteric programming language
An esoteric programming language (sometimes shortened to esolang) or weird language is a programming language designed to test the boundaries of computer programming language design, as a proof of concept, as software art, as a hacking interface to another language (particularly functional programming or procedural programming languages), or as a joke. The use of the word esoteric distinguishes them from languages that working developers use to write software.
Source: Wikipedia — Esoteric programming language (CC BY-SA 4.0)