art for art's sake

The phrase "art for art's sake " is actually related to the literary movement aestheticim whose foundation was laid in 18ths by Immanuel Kant.  Originally this phrase was used by a French writer Gautier " l'art pour l'art" in English it means "art for art sake". It was not only Gautier who who wrote those words, we can see it in the works of Edgar Allan Poe "the poetic principle "
He says, " we have taken it into our heads to write a poem simply for the poem's sake". So art for art's sake means that a true piece of art doesn't serve any didactic, moral or utilitarian function. A true work of art is complete in itself without any moral or didactic influence. 
It was actually in reaction to the Victorian moralism, Ruskin views about art  and communist realism as after the Russian revolution, a movement in painting started called "socialist realism" which was basically concerned with realist paintings of the Labour class in order to promote socialism. So art for art's sake is in reaction to all these.
This movement has been criticized by writers like Nietzsche who says,  there is no art for art sake,  arguing that the artist still expresses his/her being throgh it.
Marxists has also criticized it and say that art should be politicised for the sake of transmitting the socialist message.
The best example of art for art's sake can be seen Keats poem " ode to autumn"