What does erg mean?
An erg is a unit of energy or work belonging to the centimetre–gram–second (CGS) system, defined as the amount of work done when a force of one dyne moves an object one centimetre. It is a very small quantity by modern standards — ten million ergs make up a single joule, the standard SI unit — and although the erg has been officially superseded, it still appears in older scientific literature and in some branches of astronomy. Separately, an erg can mean a vast expanse of sand dunes in a desert, a term used by geographers to describe sandy regions such as parts of the Sahara. Both senses are nouns, and the word carries a distinctly technical, scholarly tone rather than everyday usage. Its shared root with words like 'energy' and 'ergonomics' makes it a useful reminder of how deeply the Greek concept of work is woven into scientific vocabulary.
A unit of energy or work in the CGS system, equal to 10⁻⁷ joule.
"Early twentieth-century astronomy papers often quoted stellar output in ergs per second."
Largely replaced by the joule in modern practice.
A large, relatively level area of shifting sand dunes in a desert.
"The caravan skirted the edge of the erg at dawn to avoid the midday heat."
Chiefly used in geography and geological writing about deserts such as the Sahara.
Regular plural; used for both senses.
"The star radiates billions of ergs every second."
The word 'energy' literally contains its own tiny ancestor — both trace back to the Greek 'ergon', meaning work, and it takes ten million ergs just to make one joule.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of erg
Both senses derive from different sources. The physics sense comes via German 'Erg' from Greek 'ergon', meaning work, coined in the nineteenth century for the CGS system; the same root gives English 'energy' (Greek 'energeia'), 'ergonomics', 'surgery' and 'organ'. The desert sense entered English from Arabic, where it denotes a sandy tract, and was adopted by explorers and geographers describing the Sahara.
How erg is actually used
The physics sense belongs to formal scientific register; the erg has been largely superseded by the SI joule but survives in older literature and astronomy. The desert sense is chiefly technical, used in geography and geology.
Easily confused with erg
'Erg' is a unit of energy or a sandy desert region, while 'ergo' is an adverb meaning 'therefore'.