How is one nanometer defined?

One nanometer is defined as one billionth of a meter, which is equal to (10^{-9}) meters. This measurement is commonly used in various scientific fields, particularly in nanotechnology and physics, where dimensions at the atomic and molecular levels are crucial. The significance of a nanometer lies in its utility in measuring things like the wavelength of light and the size of molecules, which are often on this small scale.

The term "nano" is derived from the Greek word "nanos," meaning "dwarf," and it plays a vital role in understanding nanoscale materials and their properties. By being one billionth of a meter, a nanometer allows scientists and engineers to precisely measure and manipulate materials that have applications in electronics, materials science, and biology, among others.

In contrast, the other options refer to different scales of measurement that do not accurately reflect the definition of one nanometer: one millionth refers to a micrometer, one thousandth refers to a millimeter, and one ten-billionth would represent a picometer, which is smaller than a nanometer.