I. noun
1. : the lowest part of the photic region of the ocean
2. : a zone lying on the border between two distinguishable fields, situations, subjects, or groups and exhibiting a blend of the characteristics of both without the distinctness of either
a kind of twilight zone between East and West, an area which declines to be dominated by either — J.C.Harsch
this twilight zone of what is implied but not actually stated — Journal of the Patent Office Society
increasing the area and the obscurity of the twilight zone which lies between state and federal functions — New Republic
3. : twilight band
II. noun
1. : twilight 2a
2. : a world of fantasy, illusion, or unreality