the.com/abyssal zone

means The ocean layer roughly 3,000 to 6,000 meters down, perpetually dark, crushingly pressurized, and near-freezing, where life exists without a trace of sunlight.

from From Greek 'abyssos,' meaning 'bottomless' (a- 'without' + byssos 'bottom, depth'). The ancient Greeks used it for any immense, unfathomable void, and the word passed through Latin into English carrying that sense of depth with no measurable floor. Oceanographers later borrowed it to name the deep-sea zone below the bathyal layer and above the trenches — fittingly, since early mariners genuinely believed such depths had no bottom at all.