Wikipedia - Velocità della luce speed of light in a vacuum

https://doi.org/10.1351/goldbook.S05854
Universal fundamental physical constant representing the speed of electromagnetic waves in vacuum; by definition $$c_{0}$$ is exactly = $$299\ 792\ 458\ \text{m s}^{-1}$$.
Source:
CODATA Bull. 1986, 63, 1 [Terms] [Book]