Wikipedia - Ordini di grannizza (vilucitati) (scn) Wikipedia - Velocità della luce (it) Wikipedia - Vełosità de ła łuxe (vec) Wikipedia - Veƚosità de ƚa luse (vec) Wikipedia - Vilucitati dâ luci (scn) Wikipedia - سرعة الضوء (ar) speed of light in a vacuum, $$c_{0}$$, $$c$$

https://doi.org/10.1351/goldbook.S05854
The speed of light in vacuum, $$c$$, is one of seven fixed constants defining the International System of Units, the SI, with $$c = 299\ 792\ 458\ \text{m s}^{-1}$$. The speed of light is considered as a fundamental constant of nature.
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 127ff [Terms] [Book]