A system of units is a set of standard measures used for the measurement of various quantities such as length, time, volume, and more. In science, there are several terms used as synonyms for system of units, including the metric system, the International System of Units (SI), and the Standard International (SI) system. The metric system is the most widely used system of units globally, which is based on the meter, liter, and gram. The SI system, on the other hand, is the modern form of the metric system, which is based on seven base units, including the kilogram, ampere, and kelvin. Lastly, the Standard International (SI) system is another term used to refer to the metric system or the SI system. Regardless of the term used, these systems are vital in standardizing measurements worldwide.