1. Sand sea in a hot desert. It is a feature of the Sahara, where sand typically is accumulated in wide shallow basins as alluvial and lacustrine deposits derived from adjacent rocky desert during the Cenozoic. It is often very large: the Grand Erg Oriental covers 196 000 km2 in Algeria and Tunisia.
2. Unit of energy or work in the c.g.s. system. 1 erg = 10−7 J.