As applied to art, means art that is innovatory, introducing or exploring new forms or subject matter
Originally a French term, meaning in English vanguard or advance guard (the part of an army that goes forward ahead of the rest): it first appeared in reference to art in France in the first half of the nineteenth century, usually credited to the influential thinker Henri de Saint-Simon, one of the forerunners of socialism. He believed in the social power of the arts and saw artists, alongside scientists and industrialists, as the leaders of a new society. In 1825 he wrote:
We artists will serve you as an avant-garde, the power of the arts is most immediate: when we want to spread new ideas we inscribe them on marble or canvas. What a magnificent destiny for the arts is that of exercising a positive power over society, a true priestly function and of marching in the van [i.e. vanguard] of all the intellectual faculties!
Avant-garde art can be said to begin in the 1850s with the realism of Gustave Courbet, who was strongly influenced by early socialist ideas. This was followed by the successive movements of modern art, and the term avant-garde is more or less synonymous with modern. Some avant-grade movements such as cubism for example have focused mainly on innovations of form, others such as futurism, De Stijl or surrealism have had strong social programmes. The notion of the avant-garde enshrines the idea that art should be judged primarily on the quality and originality of the artists vision and ideas.