Value in art is essentially how light or dark something is on a scale of white to black (with white being the highest value and black being the lowest value). It is widely considered to be one of the most important variables to the success of a painting, even more so than your selection of color (hue).
Value is one of the seven elements of art. Value deals with the lightness or darkness of a color. Since we see objects and understand objects because of how dark or light they are, value is incredible important to art. (I'll remind you that drawing and painting is about seeing.)
