abyssal zone abyssal zone /əˈbɪsəl zoʊn/

noun

1. The deep sea (2000 meters or more) where there is no light  ( abyssal zone )
   the deep sea (2000 meters or more) where there is no light
    The abyssal zone is a mysterious and largely unexplored part of the ocean.
   The abyssal zone is a mysterious and largely unexplored part of the ocean.