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.