Wikipedia - Metro 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 @S05854@ $$c$$ 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 $$\Delta\nu_\text{Cs}$$.
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019) [Terms] [Book]