Which term describes the measurement unit that is one billionth of a meter?

The term that describes the measurement unit that is one billionth of a meter is a nanometer. The nanometer is commonly used in scientific fields, particularly in nanotechnology, to measure things at an atomic or molecular scale. To put it in context, one nanometer equals (10^{-9}) meters, making it extremely useful for characterizing the size of nanoparticles, biomolecules, and other structures that are not visible to the naked eye.

In contrast, a millimeter is (10^{-3}) meters, a micrometer is (10^{-6}) meters, and a picometer is (10^{-12}) meters. Each of these units represents a different scale of measurement, and understanding their differences is crucial in various scientific and technical applications. The distinction helps clarify why the nanometer is specifically defined as one billionth of a meter.