A measurement systembased off the number 10, the size of the earth, and proprties of water. It was intruduced by French revolutionaries with the intention of creating system that was logical and easy to use, and because the previous system had been based on the feet of the king, whom they had killed.
In practical terms, one metre is a pace, half a litre is a large drink, which ways about half a kilogram, and all temperatures below -20 celsius and above 35 celsius are unbearable.
Theoretically all major nations except the united states use the metric system. In practice, all nations including the united states use a mixture of the metric system and older units.
Scientists generally use the metric system almost exclusively, but the average man on the street still finds it a bit abstract.