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 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) (http://www.bipm.org/en/publications/si-brochure/)