The centimetre-gram-second system (CGS) is a system of physical units. It is always the same for mechanical units, but there are several variants of electric additions. It was replaced by the MKS, or metre-kilogram-second system, which in turn was replaced by the International System of Units (SI), which has the three base units of MKS plus the ampere, mole, candela and kelvin.
See main article at Wikipedia:Centimetre_gram_second_system_of_units for more detrails.
This deinition is the lead from the Wikipedia article above.