Esoteric language (esolang) is not made for the purpose of mainstream programming or for communication. They are made for fun, it is also use as hacking interface for another language. They made to remove or replace conventional language features while still maintaining a language. The most popular examples are Piet, Brainfuck, Shakespeare, Begungs, LOLCODE, whitespace, INTERCAL and Chef.
The earliest example of an esoteric language was INTERCAL, it was designed in 1972 by Don Woods and James M.
The reasons for making esoteric programming languages are ostensibly to make an intellectual point about language construction or language use. However, they perform an in-programmer function, nerd-like, some would say, of demonstrating how weird a programme can be, in many cases a highly skilled and - yes - esoteric joke.
These languages are not intended to be communicative (almost the opposite) and ideally should have as few instructions as possible and be very difficult to programme in. Brainfuck was possibly the earliest example, the name speaking for itself.