In general, any artistic approach in which the outer world is represented as faithfully to appearances as possible. In a more specific sense, an artistic movement, prevalent in Europe and the USA in the second half of the 19th century, that prized the accurate representation of nature and adhered to themes of daily life.  Although naturalism is often used interchangeably with the term realism, there is a difference between them. The realism of Gustave Courbet is more interested in the honest and blunt depiction of subjects and situations, while the naturalism of Ernest Meissonier is more a visually accurate depiction of subjects, which in other hands might well have been depicted ideally.