twilight zone

(noun) the lowest level of the ocean to which light can reach. Synonyms: twilight zone.

(noun) the ambiguous region between two categories or states or conditions (usually containing some features of both). Synonyms: twilight zone, no man's land. Examples: "But there is still a twilight zone, the tantalizing occurrences that are probably noise but might possibly be a signal." "In the twilight zone between humor and vulgarity." "In that no man's land between negotiation and aggression."