Vacuum

E = mc2 ==> E = energy / m = mass / c2 = speed of light squared

c2 = 299.792.458 m/s2

c comes from latim celeritas (speed)

The speed of light in a vacuum is exactly 299.792.458 m/s or 1.079.252.848,8 km/h. Vacuum is a volume of space substansively empty of matter, so that gaseous pressure is much less than standard atmospheric pressure. Space can never be perfectly empty.