FORM SHADOW:  The form shadow is the area of the object itself that is darkened by shadow; little or no light is presented because it is on the side of the object opposite the light.

CAST SHADOW: The cast shadow is the shadow that is projected by the object onto an adjacent surface

HIGHLIGHT: The highlight is the area of the object that is directly illuminated because it is closest to the light source.

HALFTONE: The halftone is the transparent portion of shadows and highlights. It is used to represent the transition from the color and value of the surface toward either dark or light. Of course, a different color and value are used to express each type of halftone, one for the shadow halftone, and one for the highlight halftone

ACCENT: The accent is the most concentrated, most opaque portion of shadows and highlights. It is used to represent the darkest (within the shadow) and the brightest (within the highlight) areas of an object

REFLECTED LIGHT: In addition to a halftone and an accent within almost every form shadow lies reflected light. Reflected light is the light that is reflected back onto an object from the adjacent surface. This area of a shadow is generally expressed as the same color or value as the halftone shadow; it is usually not as light as any portion of the highlight.