Which prefix in the metric system indicates 1 millionth of the standard unit?

The prefix that indicates 1 millionth of the standard unit in the metric system is micro. In metric terminology, micro is represented by the Greek letter "µ" and signifies a factor of 10^-6. This means that one micro unit (e.g., one micrometer) is equal to one millionth of a meter, or 0.000001 meters. Understanding this prefix is essential for working with measurements in fields such as bioscience and other scientific disciplines, where small quantities are often involved.

Other prefixes like milli, nano, and pico denote different powers of ten: milli corresponds to 10^-3 (one thousandth), nano to 10^-9 (one billionth), and pico to 10^-12 (one trillionth). Each of these prefixes is useful in various contexts but does not represent the millionth part, making micro the precise choice for this question.