A metric prefix is a unit of measurement that modifies the value of a base unit in the metric system. These prefixes indicate multiples or fractions of the base unit, making it easier to express large or small quantities. For example, the prefix kilo- represents a factor of one thousand, so one kilometer (km) equals 1,000 meters (m). Common metric prefixes include centi- for one-hundredth (0.01) and milli- for one-thousandth (0.001). These prefixes help simplify communication in science, engineering, and everyday life by providing a clear and standardized way to express measurements across various scales.