SI in science stands for International System of Units or System international.

It is the world's most widely used system of measurement.

SI is a scientific expression of quantities or magnitudes of important natural phenomena.

It is the modern form of a metric system. There are seven base units in SI, from which other units are derived.

SI defined the standard units of measurement for the seven base quantities.

The seven SI base units are second for time, meter for length, kilogram for mass, ampere from electric current, kelvin for temperature, a mole for amount of substance, and candela for luminous intensity.

The other SI units are derived by multiplying the different powers of the base units.