twilight zone

Noun

• the ambiguous region between two categories or states or conditions (usually containing some features of both)
  • 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
    

• the lowest level of the ocean to which light can reach