WordWeb Online

1. The lowest level of the ocean to which light can reach
    
2. The ambiguous region between two categories, 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 humour and vulgarity";
   - no man's land

Derived forms: twilight zones

Type of: ambiguity, Davy Jones, Davy Jones's locker, equivocalness, ocean bottom, ocean floor, sea bottom, sea floor, seabed

Encyclopedia: Twilight zone