What prefix in the metric system indicates 1 thousandth of the standard unit?

The prefix that indicates one thousandth of the standard unit in the metric system is "milli." In metric terminology, "milli-" represents a factor of 10^-3, which means that one milli-unit is equal to one thousandth of a full unit. For example, in the case of a millimeter (mm), there are 1,000 millimeters in a single meter.

Understanding this prefix is crucial for converting and comparing measurements in scientific contexts, especially in fields such as biology, where precise measurements are often needed. The other prefixes—such as "centi," which denotes one hundredth of a unit, "micro," representing one millionth, and "kilo," indicating one thousand times the unit—represent different scaling factors and are not synonymous with "one thousandth."