Here's why:

* Abyssal refers to the deep ocean, specifically the depths between 3,000 and 6,000 meters.

* Plains indicate a flat, expansive area.

Abyssal plains are formed by the accumulation of sediments, primarily fine-grained mud and ooze, over millions of years. These sediments are transported by ocean currents and slowly settle to the bottom, burying any underlying features and creating a smooth, flat surface.