The depression in the ocean floor where one tectonic plate is subducting beneath another is called an oceanic trench. Oceanic trenches are long, narrow, and very deep topographic depressions formed at convergent plate boundaries where an older, denser oceanic plate is forced under a lighter plate, either oceanic or continental, in a process known as subduction

. These trenches typically measure 50 to 100 kilometers wide and can be several kilometers deep, often forming a steep, V-shaped trench on the seafloor. The trench marks the location where the subducting plate begins to descend into the mantle beneath the overriding plate

. Examples include the Mariana Trench, which reaches depths of nearly 11 kilometers below sea level

. Thus, the oceanic trench is the surface expression of the subduction zone on the ocean floor, associated with intense geological activity such as earthquakes and volcanic arcs