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 , meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than 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 and contains several ergs, such as the Chech Erg  and the Issaouane Erg  in Algeria. Approximately 85% of all the Earth's mobile sand is found in ergs that are greater than . Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan.