What is the full form of SI?

SI units are internationally accepted units. It stands for 'Système international' in French.

For example, you can measure mass in grams, kilograms, tons, etc. But the SI unit of mass is kg. Similarly, the temperature can be measured in Celsius, Fahrenheit, Kelvin, etc. But its SI unit is Kelvin. The SI units are sometimes also known as MKS units(meter, kilogram, and second). In 1939, the CCE recommended the adoption of Internation units and got approval.