Erg/ɜːrɡ/ Definition 1 of 2Pro Tip 1/3Physics Measure An 'erg' is a tiny amount of energy, much smaller than a joule. Her experiment released millions of ergs in only a few seconds. Pro Tip 2/3Technical Term Used mainly in scientific contexts, not in everyday conversation. The energy emitted equaled 500 ergs. Pro Tip 3/3Precision Required When discussing work or energy in physics, precision is key, so use 'ergs' accurately. That small reaction yielded about 150 ergs.