Erg

Erg is a term with multiple meanings in science and geography. In physics, it is a unit of energy in the centimetre–gram–second (CGS) system. An erg is defined as the work done by a force of one dyne acting over a distance of one centimeter. Since a dyne is g·cm/s², one erg equals 1×10^-7 joule. The erg is a very small unit by modern standards, and joule-based units are usually preferred. The term derives from the Greek ergon, meaning work, and is used in discussions of CGS energy units such as CGS-EMU or CGS-ESU and in some astrophysical contexts.

In geography, an erg is a broad, flat area of desert covered with wind-sculpted sand dunes. The word, drawn from Arabic and French usage, is used to describe dune seas such as the Grand Erg Oriental and Grand Erg Occidental of the Sahara. Ergs can span hundreds to thousands of square kilometers and are typically bordered by other desert terrains such as regs (gravel plains) and hamadas (rocky plateaus).

In addition to these, “Erg” can appear as a surname or place name in various contexts, but the two primary definitions—energy unit in CGS physics and a dune-filled desert region—are the most widely recognized.