The Free Dictionary:
outsider artist
"Work produced by artists who do not fit the traditional standards laid down by the dominant art establishments of an era. The power, influence, and position of such establishments enable them to decide what is acceptable as art in society. At various times throughout art history, groups such as women, ethnic minorities, peasants, and the lower classes have been marginalized and considered ‘outsiders’. In today's art world, those labelled as outsiders may include artists who have not received official training, or associated themselves with a recognized art system."
The Coming In of Outsider Art
article by Audrey Regan
"Outsider art is not determined as much by the artwork itself as by the set of circumstances that were present in the life of the artist when the art was made. Once the outsider artist is "discovered", he can no longer be classified as one who creates art for his own use, for he is now sharing his art with the public. He can no longer be described as one who is unaware of the art being made by others as he is now a part of the very artworld he once knew nothing about and will be influenced by it. Eventually, he may stop using the materials of his everyday life, when demand for his work necessitates the use of more effective and readily available materials."
A CULTURAL ANTHROPOLOGY: The Nameless Art of a Scrapheap Subculture
by Tori Orr
"...Ultimately it is an error to perceive outsider artists as eccentrics who act in supposed isolation. Many use their wondrous art in order to create a link with society. And to say they are unskilled and naive misses the point. Most may be self-taught but rely on skills picked up from others. Their art is neither psychotic nor accidental. It is simply inspired. As Howard Finster is fond of saying, 'all ideas are visions'."