Base units are the fundamental units of measurement in the International System of Units (SI). They serve as the building blocks for all other measurements and are defined independently of other units. There are seven base units, including the meter for length, the kilogram for mass, and the second for time. Each base unit is linked to a specific physical quantity, ensuring consistency and accuracy in scientific measurements. For example, the base unit of temperature is the kelvin, while the base unit of electric current is the ampere. These units provide a standardized way to communicate measurements across various fields, including science and engineering.