noun
abyssal plain
Oceanographic term for a flat or gently sloping area of the deep ocean floor, typically at depths of 2,200–5,500 meters.
深海平原は、大陸棚の外側に広がる平坦な海底地形である。
Abyssal plains are flat seafloor features that extend beyond the continental shelf.
Compound of 深海 (deep sea) and 平原 (plain), directly describing a flat area of the deep ocean floor.