An erg is a large area of sand that has little or no vegetative cover at all. Sand covers more than '20%' of the area in an erg.
Most of the sand is wind-blown and form small dune fields. Several ergs may be present in a desert which is an area that has large number of sand dunes.
An erg is also called a 'sand sea' or a 'dune sea' and is usually a flat and broad area of a desert.
