The term Outsider Art was coined by art critic Roger Cardinal in 1972 as an English synonym for Art Brut (which literally translates as "Raw Art" or "Rough Art"), a label created by French artist Jean Dubuffet to describe art created outside the boundaries of official culture; Dubuffet focused particularly on art by insane asylum inmates.

While Dubuffet's term is quite specific, the English term "Outsider Art" is often applied more broadly, to include certain self-taught or Naïve art makers who were never institutionalized. Typically, those labeled as Outsider Artists have little or no contact with the institutions of the mainstream art world; in many cases, their work is "discovered" only after their deaths. Much Outsider Art illustrates extreme mental states, unconventional ideas, or elaborate fantasy worlds.

Outsider Art has emerged as a successful art marketing category (an annual Outsider Art Fair has taken place in New York since 1992); thus the term is sometimes misapplied as a catch-all marketing label for art created by people outside the "art world" mainstream, regardless of their circumstances or the content of their work.