The SI unit, or International System of Units (SI), is the modern form of the metric system and the world's most widely used system of measurement. It is used globally in science, technology, industry, and everyday commerce
. The SI system is based on seven fundamental base units, each corresponding to a basic physical quantity:
- Second (s) for time
- Metre (m) for length
- Kilogram (kg) for mass
- Ampere (A) for electric current
- Kelvin (K) for thermodynamic temperature
- Mole (mol) for amount of substance
- Candela (cd) for luminous intensity
These base units are defined by exact values of seven defining constants of nature, such as the speed of light, Planck constant, and the hyperfine transition frequency of the cesium-133 atom, ensuring precision and universality
. The SI system also includes coherent derived units formed by combining base units and uses decimal-based prefixes to express multiples or fractions of these units conveniently
. In summary, the SI unit system provides a standardized, internationally agreed framework for measuring physical quantities, facilitating clear communication and consistency worldwide
