penumbra: Meaning and Definition of

pe•num•bra

1. the partial or imperfect shadow outside the complete shadow of an opaque body, as a planet, where the light from the source of illumination is only partly cut off. Cf.umbra(def. 3a).
2. the grayish marginal portion of a sunspot. Cf.umbra(def. 3b).
2. a shadowy, indefinite, or marginal area.