twilight zone

WordReference Random House Unabridged Dictionary of American English © 2026

twi′light zone′, 

1. Oceanography the lowest level of the ocean that light can reach.
2. an ill-defined area between two distinct conditions, categories, etc., usually comprising certain features of both;
   an indefinite boundary:
   a twilight zone between fantasy and reality.
• 1905–10

Collins Concise English Dictionary © HarperCollins Publishers::

twilight zone noun

1. any indefinite or transitional condition or area
2. an area of a city or town, usually surrounding the central business district, where houses have become dilapidated