I found the following definitions at www.artlex.com,
a great resource site for anyone interested in the arts. Another great site is
of American Folk Art in the Big Apple, they're filled with fine examples of
American craft, folk art, and "outsider" art., visionary and
Folk art - Art made by people who have had little or no formal schooling in art. Folk artists usually made works of art with traditional techniques and content, in styles handed down through many generations, and often of a particular region. Paintings, sculptures, ceramics, metal work, costume, tools, and other everyday objects all may be folk art.
Naive art or na´ve art -The style of naive painting is characterized by a careful, simplifying approach, non-scientific perspective, bright colors, and often, an enchantingly literal depiction of imaginary scenes. Although not following any particular movement or aesthetic, naive painters have been a continuing international phenomenon and influence since the beginning of the twentieth century. The term usually refers to works produced by artists (also called naifs or na´fs) who had no formal training. Their apparent affinity with non-Western art and their bold expressive qualities made them appealing to the early modernists searching for new forms of expression. The art of naive artists is sometimes referred to as primitive art, but is now most commonly called outsider and folk art.
Outsider art or outsider art and Outsiders or outsiders- Strictly interpreted, outsider art refers to works by those outside of mainstream society. In the United States, outsider art broadly includes folk art and ethnic art as well as by prisoners, the mentally ill and others neither trained in art nor making their works to sell them. In Europe, outsider art is more narrowly interpreted as art by the mentally disturbed. The term naive was once applied to this work, but is no longer considered current. Because fewer and fewer people are sufficiently isolated to be truly outsiders, most are either mentally ill or working far from urban art scenes.
Art brut- French for "raw art," Jean Dubuffet (1901-1985) devised this name in 1945 for the art of children and outsiders (naive artists and the mentally ill); actually, anyone not producing art for profit or recognition. Because they did not adhere to the cultural norms or fashion effecting most artists, Dubuffet felt there was greater honesty and power inherent in the work of such people. His collection of art brut moved Dubuffet to cultivate such raw artistic elements in his own work, sometimes making pictures with pastes including mud, asphalt, or broken glass.