An erg (also sand sea or dune sea, or sand sheet if it lacks dunes) is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover. The term takes its name from the Arabic word ʿarq (عرق), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than 125 square kilometres (48 sq mi) of aeolian or wind-blown sand and where sand covers more than 20% of the surface. Smaller areas are known as "dune fields". The largest hot desert in the world, the Sahara, covers 9 million square kilometres (3.5×10^⁶ sq mi) and contains several ergs, such as the Chech Erg (24.57°N 2.59°W) and the Issaouane Erg (31.18°N 7.93°E) in Algeria. Approximately 85% of all the Earth's mobile sand is found in ergs that are greater than 32,000 square kilometres (12,000 sq mi).