To apply a thin and transparent (and usually darker) color over another (and usually lighter) color to modify its appearance, making a red more violet for instance, or to create a new color. Glazing blue over yellow for example makes green. Artists usually glaze at the end of a painting to modify tones in subtle increments and to unify the work. This has the advantage of oiling the surface for oil paintings and follows the general principle of fat over lean. Acrylic artists also glaze their work as needed, using one of the acrylic mediums to achieve the desired sheen. Because acrylic is crystal clear, more layers and various thickness glazes can be applied. I have used as many as 20 layers of yellow and orange glazes over a painted light to give the effect of the inner glow from the light. This would not be recommended in oil.