What is meant by the international system of units?

Answer 1

In the United States we use US, or Customary Units, like inches, feet, etc. In most other countries they use the international system, or SI, units, like meters, kilometers, etc. In the SI system conversions are made in multiples of 10, making it simpler

Answer 2

The "International System", abbreviated as SI (from the French initials), is the system of units used in most countries all over the world. It is also known as the "metric system"; however, there are actually several metric systems - the version called the SI is the one used nowadays (as of 2016) all over the world.