Erg

An erg is a broad, flat expanse of desert covered in wind swept sand with little or no plant cover, its name drawn from the Arabic word irq, meaning dune field; formally, an erg must cover more than 125 square kilometers of aeolian sand with dunes over at least a fifth of its surface, with smaller sandy areas classed instead as dune fields. The largest hot desert on Earth, the Sahara, holds many of the largest ergs, including the Chech Erg and the Issaouane Erg in Algeria, and roughly 85 percent of all the planet's mobile sand lies within ergs larger than 32,000 square kilometers, the largest of which is the Rub' al Khali, the Empty Quarter of the Arabian Peninsula. Similar sand sea landforms have also been observed on other worlds, including Venus, Mars and Saturn's moon Titan.