Answer:
Abyssal plain
Step-by-step explanation:
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 9,800 ft and 20,000 ft.
They are among the flattest, smoothest, and least explored regions on Earth.
The creation of the abyssal plain is the result of the spreading of the seafloor and the melting of the lower oceanic crust. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt.