The base unit of mass in the International System of Units (SI) is the kilogram. The kilogram is defined as the mass of a specific platinum-iridium cylinder known as the International Prototype of the Kilogram, which was kept at the International Bureau of Weights and Measures in France. However, in 2019, the definition was updated to be based on fundamental physical constants, specifically the Planck constant. The kilogram is a fundamental unit in various scientific measurements and is used globally for commerce, industry, and everyday activities, providing a standard reference for measuring weight.