Penumbra (noun)

1. The partially shaded outer region of a shadow cast by an opaque object, where only part of the light source is blocked.
2. A marginal or fringe area that is adjacent to or surrounding a central or dominant area.

Origin:

From latin paene 'nearly' + umbra 'shadow'.

Examples:

1. The penumbra of the moon during an eclipse is visible as a lighter, outer part of the shadow on the earth.
2. The penumbra of the city was characterized by small, run-down neighborhoods.
3. In physics, the penumbra region is important in understanding the behavior of light.
4. The penumbra of the forest provided ample opportunities for wildlife to thrive.
5. The penumbra of the sun's shadow during a solar eclipse can be observed as a reddish fringe on the earth.