Chiaroscuro is a technique in painting that uses tones, shades, shadows and highlights to create the illusion of three dimensions on two dimensional media. Developed in the Renaissance, chiaroscuro comes from the Italian words for bright or clear and dark or obscure. It is usually translated as 'light-dark'.
It is difficult today to realize how revolutionary the concept and application of chiaroscuro techniques must have been when they were first developed. Prior to the Renaissance, with its ferment of intellectual activity, painting as an art was what we would now characterize as 'primitive'. Shapes were delineated with outlines, and colors were flat planes, cartoonish by today's standards.
Chiaroscuro may sound simplistic, yet most people cannot easily reproduce a colored object with a 3-dimensional feel because the brain, in a sense, 'overprocesses' what the eyes see. A black car on a sunny day is a perfect illustration — it will reflect blue hues from the clear sky and other colors from its surroundings, including the colors of any cars nearby. Yet most people will subtract out the reflected lights and shadow and 'see' the car as simply black.
A primitive painter might paint a shiny red bowl on a blue tablecloth as a flat crescent of red, perhaps with a black outline. The painter adept at chiaroscuro would incorporate white or yellow highlights at the point of the bowl closest to the light source, and the parts of the bowl unlit by the light would perhaps be maroon, deepening to brown or black. The blue cloth would reflect a blue tint onto the bottom of the bowl, light on the light side and darker on the side away from the light.
All artists since the Renaissance have been influenced by the development of chiaroscuro techniques. Since modeling three dimensions on flat surfaces via shading and highlighting is the standard today, rather than a radical departure, the term chiaroscuro is typically now reserved for very dramatic uses of contrasting light and darkness. The painter most often associated with chiaroscuro is Michelangelo Merisi da Caravaggio, who is usually referred to by his 'town-name' Caravaggio, possibly to prevent confusion with another Michaelangelo.