penumbra

1. (astronomy) A region around the edge of a sunspot, darker than the sun's surface but lighter than the middle of the sunspot.

2. (figuratively) An area of uncertainty or intermediacy between two mutually exclusive states or categories.Examples: "These firms or businesses are not illegal in the strict sense, but there is a shadowy penumbra within which they live, and it is often convenient for the government to look the other way."; "[…] God chose to descend into the realm of human imperfection, where the light of truth is spare and must exist in the penumbra of partial knowledge mixed with partial ignorance."; "Unlike some of his contemporaries Parkes never implied that the Irish were close, in the racial hierarchy, to black, condemned to some racial penumbra, between black and white; but nor, given Catholic exclusion from the given traditions of his native radicalism, were the Irish white in the same way that he was."Synonyms: grey areafiguratively

3. (figuratively) An area that lies on the edge of something; a fringe.Examples: "Whilst the orthodox, de-charismatized churches steadily lose influence and support and the new cults develop, in the religious penumbra there have persisted, during the last century, echoes of charisma."; "But for all the expansionist energy of a metro area that sprawls from Wisconsin to Indiana (total population: 7.2 million), downtown Chicago and its penumbra also stand rejuvenated."; "Some are accounts of the latest advances, but too many are in that weary penumbra of science inhabited by sociologists, who wander like children in a toyshop, playing with devices they scarcely understand."Synonyms: periphery, outskirtfiguratively

4. (medicine, preceded by "ischaemic", after a stroke) A region of the brain that has lost only some of its blood supply, and retains structural integrity but has lost function.