The centimeter-gram-second system (abbreviated cgs) of physical units of measure is a nearly obsolete system that was in widespread use in the nineteenth century, until the meter-kilogram-second system (mks), with its much larger units, replaced it. The main distinguishing feature of the cgs system is that most of its units are named for the physical properties they are supposed to measure, rather than for famous scientists, as is the case with the mks and SI systems.
The one unit that cgs shares with SI is the unit of time, the second. Its definition history is the same as for the SI second.
The cgs unit of length is the centimeter, or one-hundredth of a meter.
The cgs unit of mass is the gram. Originally (see Metric system) this was the primary unit of mass. Today a gram is defined as one-thousandth of a kilogram.
The cgs unit of force is the dyne (from the Greek δύναμαι or dunamai I can). One dyne is the amount of force needed to accelerate a one-gram mass one centimeter per second per second.
The cgs unit of pressure is the barye. One barye exerts one dyne of force on every square centimeter of area.
Work and power
The cgs unit of work and energy is the erg (from the Greek εργον or ergon work). One erg is the amount of work done when exerting a force of one dyne over one centimeter, or the energy required to do that work.
The cgs system does not, properly speaking, have a separate unit of power. Instead, it expresses power in ergs per second.