A system of measure initially based on: The circumference of the Earth, the freezing and boiling points of water under 1 atm, the density of water at 4oC, the specific heat capacity of water, rotational period of the Earth, and a number of other things. It uses powers of ten for the relationships between as many units as possible. It was developed during the French Revolution. The two main variants of Metric are mks/SI and cgs. Only the most backward of countries cling to antiquated systems like Imperial and it's derivative US Standard.