## metre, $$\text{m}$$

https://doi.org/10.1351/goldbook.M03884
The metre, symbol $$\text{m}$$, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in a vacuum c to be $$299\ 792\ 458$$ when expressed in the unit $$\text{m s}^{-1}$$, where the second is defined in terms of the caesium frequency Δν(Cs).
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019) (http://www.bipm.org/en/publications/si-brochure/)