A nanometre is a unit of length in the metric system, equal to one billionth of a metre.
It is one of the more often used units for very small lengths, and equals ten Ångström, an internationally recognised non-SI unit of length. It is often associated with the field of nanotechnology and the wavelength of light. Formerly, millimicron (symbol mµ) was used for the nanometre. The symbol µµ has also been used.
It is also the most common unit used to describe the manufacturing technology used in the semiconductor industry. It is the most common unit to describe the wavelength of light, with visible light falling in the region of 400–700 nm.