I believe it is the Marianas Trench.
The abyssal plains are flat or very gently sloping areas of the deep ocean floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains generally lie between the foot of a continental rise (shelf) and a mid-oceanic ridge.
Large flat areas of the ocean floor are called abyssal plains. These regions are typically covered in thick layers of fine sediment and are among the flattest, most featureless parts of the ocean floor. Abyssal plains are found at depths between 3,000 and 6,000 meters.
The abyssal plain is typically located at depths between 3,000 and 6,000 meters (9,800 and 19,700 feet) below the ocean's surface. It is one of the flattest and most featureless regions on Earth, covering vast areas of the ocean floor.
Flattest.
flatter/flattest
which landforms are on the ocean floor
The topography of the ocean floor
The ocean surface represents the flattest part of Earth's surface since water seeks its own level due to gravity, creating a smooth and relatively uniform surface.
The ocean floor is not smooth.The ocean floor is made up of rocks, ledges and ditches.
blank are found on the ocean floor
marine organisms
Ocean floor