Which metric prefix represents one-thousandth of a unit?

The metric prefix that represents one-thousandth of a unit is "milli." In the metric system, each prefix denotes a specific fraction or multiple of a unit based on powers of ten. The prefix "milli-" specifically indicates a factor of 10^-3, or one-thousandth. This means that when you attach "milli-" to a unit, you are effectively dividing that unit into 1,000 equal parts.

For example, one millimeter is one-thousandth of a meter, and one milliliter is one-thousandth of a liter. This systematic approach in the metric system allows for easy conversions and helps in scientific calculations where precise measurements are crucial. Understanding the meaning of "milli-" helps to navigate various scientific contexts and ensures clarity when measuring smaller quantities.