The term "value" in art refers to the lightness and darkness of a color. One of its uses is in rendering light and shadow in two-dimensional artwork. It also helps create a focal point in a painting as the human eye is drawn to areas of high contrast.
A good range of values in a piece of art helps create a three-dimensional illusion. Values that are too similar make the artwork appear flattened and the objects in the painting seem close together. Contrasting values are used in a wide variety of artistic styles, from realistic to abstract. Some modern artists, like Kazimir Malevich, use high-contrasting values to simulate movement in his Cubo-Futurist art.