The cgs full form is centimetre-gram-seconds. The centimetre–gram–second (abbreviated CGS or cgs) system of units is a variation of the metric system that uses the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are explicitly derived from these three foundation units, however the CGS system was extended in a variety of ways to include electromagnetism.
C = Centimetre
G = Gram
S = Seconds
The CGS system was substantially replaced by the MKS system, which was extended and replaced by the International System of Units, which was based on the metre, kilogram, and second (SI). SI is the only system of units used in many sectors of research and engineering, while CGS is still widely used in several subfields.
Converting between CGS and SI in measurements of electromagnetic phenomena (including units of charge, electric and magnetic fields, voltage, and so on) is more subtle. The form of formulas for physical laws of electromagnetic (such as Maxwell’s equations) varies depending on the unit system utilized.
This is due to the fact that electromagnetic values in SI and CGS are defined differently, whereas mechanical quantities are defined the same way.
Furthermore, there are multiple viable ways to define electromagnetic quantities inside CGS, resulting in various “sub-systems,” such as Gaussian units, “ESU,” “EMU,” and Lorentz–Heaviside units. Gaussian units are the most used today, and the term “CGS units” is often used to refer to CGS-Gaussian units.