The accepted value for the speed of light in a vacuum is precisely 299,792,458 meters/second.

This value is derived from two other defined values -- the exact value of a secondis "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom" and from the meter being defined as the distance light travels in a vacuum in 1/299792458 of a second.^*

In a Bose-Einstein condensate, the speed of light has been made to go as slow as 17 meters/second.

* - in other words, a meter is defined by the speed of light in a vacuum and not the other way around.