Marcel Duchamp's Urinal
Avant garde (sometimes avant-garde; literally, vanguard) is a French language phrase, one of a number of French phrases used by English speakers. It is used to refer to persons or actions that are novel or experimental, particularly with respect to the arts. See for example: dadaism, cubism, futurism, lettrisme, paradoxism, neoism, etc.
Surrealism claims to have transcended the "avant-garde."
The avant garde was originally concerned with art for the sake of social progress: seeing the artist as the vangard of a social reform movement. Over time however the term has also come to be associated with movements concerned with "art for art's sake", concerned directly with aesthetic experience rather than social reform, the direct opposite of its original intentions.
See also: Experimental music