Naturalism in art refers to the depiction of realistic objects in a natural setting. The Realism movement of the 19th century advocated naturalism in reaction to the stylized and idealized depictions of subjects in Romanticism, but many painters have used a similar approach over the centuries. One example of Naturalism is the artwork of American artist William Bliss Baker, whose landscape paintings are considered some of the best examples of the naturalist movement. Another example is the French Albert Charpin, from the Barbizon School, with his paintings of sheep in their natural settings.
Naturalism began in the early Renaissance, and developed itself further throughout the Renaissance, such as with the Florentine School.
Naturalism is a type of art that pays attention to very accurate and precise details, and portrays things as they are.
Source: wikipedia