The prefix "milli-" is a metric unit prefix that denotes a factor of one thousandth, or 0.001. It is commonly used in measurements to indicate a smaller scale, such as in millimeter (one thousandth of a meter) or milligram (one thousandth of a gram). This prefix helps simplify calculations and comparisons in scientific and everyday contexts. In the metric system, "milli-" is part of a standardized set of prefixes that help express quantities in a clear and consistent manner. Other prefixes include centi- (one hundredth) and kilo- (one thousand). Using "milli-" allows for precise communication in fields like science, engineering, and medicine.