nm refers to the wavelength of the light source used by the lithography machine, usually 365nm, 248nm, 193nm, and so on.
Where, the shorter the wavelength represents the higher the energy, for the production of smaller chips, you need to use a shorter wavelength light source. At present, the most advanced semiconductor manufacturing, 13.5nm of extreme ultraviolet light (EUV) has been used, this wavelength can make denser, smaller transistors and capacitors, help improve chip performance and power consumption, is the trend of future chip manufacturing.
It refers to the smallest size of transistor that can be made, with 1nm equal to one billionth of a meter