Which metric prefix represents one millionth?

The metric prefix that represents one millionth is micro. In the International System of Units (SI), the prefix "micro-" is denoted by the Greek letter "μ" and indicates a factor of 10^-6. Therefore, when a measurement has the prefix micro in front of it, such as microgram or micrometer, it is one millionth of the base unit.

The other prefixes—nano, centi, and milli—represent different values. "Nano-" denotes one billionth (10^-9), "centi-" represents one hundredth (10^-2), and "milli-" means one thousandth (10^-3). These prefixes are part of a systematic way to define and scale measurements in the metric system, allowing for clearer communication of quantities and measurements across scientific disciplines.