The Sahara (, , ‘the Great Desert’) is the largest subtropical hot desert and third largest desert after Antarctica and the Arctic. At over , it covers most of North Africa, and is nearly the area of China or the United States. The Sahara stretches from the Red Sea in the east, including parts of the Mediterranean, to the Atlantic Ocean in the west. To the south, it is delimited by the Sahel, a belt of semi-arid tropical savanna that composes the northern region of central and western Sub-Saharan Africa. Some of the sand dunes can reach in height. The name comes from the plural Arabic language word for desert ( ).