The International System of Units (SI) is a global system used for measurements, commonly known as the metric system.
The 3 main units are:
• meter
• kilogram
• second
And there are 4 more that complete the system:
• ampere (electrical current)
• kelvin (temperature)
• mole (amount of substance)
• candela (luminous intensity)
There are many, many more "derived units" that are defined using the seven base units.
See: Metric System, Unit