What are abyssal plains characterized as?

Abyssal plains are defined as flat and expansive underwater areas that lie at significant depths in the ocean, typically between 3,000 and 6,000 meters (about 10,000 to 20,000 feet) below the surface. These plains are characterized by their smooth and nearly featureless topography, which results from the accumulation of sediment that has settled over time, covering any irregularities on the ocean floor, such as hills or mountains.

Their flatness distinguishes them from other underwater features, such as rugged seafloors, which may have significant topographical changes due to tectonic activity or volcanic formations. This unique characteristic of being flat makes abyssal plains some of the most extensive habitats on Earth, often covering more than 50% of the ocean's surface. While options like submarine volcanoes, rugged ocean seafloors, and coral reefs represent specific geological or ecological features, they do not capture the defining characteristic of abyssal plains, which is their flatness and wide expanse on the ocean floor.