The continental margin is the zone of the ocean floor that separates the thin oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

 from thick continental crust

Continental crust

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...

. Continental margins constitute about 28% of the oceanic area.

The transition from continental to oceanic crust commonly occurs within the outer part of the margin, called continental rise. Oceanwards beyond the edge of the rise lies the abyssal plain

Abyssal plain

An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 metres. Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface. They are among the flattest, smoothest...

. The underwater part of the continental crust is called continental shelf

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

, which usually abruptly terminates with the continental slope, which in turn terminates with the foot of the slope. The under-ocean part constitutes about 20% of the continental crust.

The edge of the continental margin is one criterion for the boundary of the internationally recognized claims to underwater resources by countries in the definition of the "Continental Shelf"

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

 by the United Nations Convention on the Law of the Sea

United Nations Convention on the Law of the Sea

The United Nations Convention on the Law of the Sea , also called the Law of the Sea Convention or the Law of the Sea treaty, is the international agreement that resulted from the third United Nations Conference on the Law of the Sea , which took place from 1973 through 1982...

(although in the UN definition the "legal continental shelf" may extend beyond the geomorphological continental shelf and vice versa).