Erg is a unit of measurement used in the field of physics to quantify energy or work. It is defined as the amount of work done when a force of one dyne is applied over a distance of one centimeter. The erg is part of the CGS (centimeter-gram-second) system of units, which is less commonly used today compared to the SI (International System of Units). In practical terms, one erg is a very small amount of energy. For example, it takes about 4.184 joules to equal one calorie, which means that one erg is equivalent to 10^-7 joules. This makes the erg useful primarily in scientific contexts where small energy values are relevant.