subsurface scattering
Subsurface scattering is the effect whereby light penetrates the surface of a material, such as skin or hair, and scatters beneath the surface before re-emerging on the other side, reflecting the color of the inside material. Imagine holding a flashlight up to your hand. The light doesn't just reflect off the surface but also partially enters and scatters beneath the skin, illuminating it from within and giving it a soft, red glow.