The prefix used in the metric system to denote one billionth is nano-. This prefix is derived from the Greek word “nanos,” meaning “dwarf.” In scientific terms, it signifies a factor of 10^-9. The nanometer (nm) is a common unit that utilizes this prefix, often used to measure atomic and molecular scales, particularly in fields like nanotechnology and materials science. The use of this prefix allows for precise communication about measurements that involve very small dimensions, contributing to advancements in science and engineering.