shading shading /ˈʃeɪdɪŋ/

noun

1. () A gradation involving small or imperceptible differences between grades  ( blending , shading )
   a gradation involving small or imperceptible differences between grades
   
2. () Graded markings that indicate light or shaded areas in a drawing or painting  ( shading )
   graded markings that indicate light or shaded areas in a drawing or painting