Shadow நிழல்
The dark shape left where an object blocks light from reaching a surface.
See it in Depth terrain. Try a sample map, then lower Sun height until the hills throw long shadows.
In plain words
Light travels in straight lines, so anything in its way leaves a dark patch behind it. That patch is a shadow. A low sun makes long shadows, and a high sun makes short ones. Shadows tell your eyes where things are and how they touch the ground. To draw them, a computer checks whether each point can see the light.