SI prefixes are symbols added to the base units of the International System of Units (SI) to indicate multiples or fractions of those units. For example, the prefix kilo- represents a factor of 1,000, so 1 kilometer (km) equals 1,000 meters (m). Other common prefixes include centi- for one-hundredth (0.01) and milli- for one-thousandth (0.001). These prefixes help simplify communication in science and engineering by providing a clear way to express large or small quantities. They are standardized, making it easier for people worldwide to understand measurements. For instance, mega- denotes one million (1,000,000), while nano- signifies one billionth (0.000000001).