Penumbra /(?)/

Pe·num·bra

Penumbra

n.
  1. An incomplete or partial shadow.
  2. The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light. (Astron.)
  3. The part of a picture where the shade imperceptibly blends with the light. (Paint.)