What speed is always measured for light in a vacuum, regardless of the observer's speed?

Answer

Symbolized as $c$

The speed of light in a vacuum, $c$, is a non-negotiable number that observers always agree upon, no matter their own speed or the speed of the light source they are measuring.

What speed is always measured for light in a vacuum, regardless of the observer's speed?

#Videos

I finally understood why speed of light is a constant! (My mind is blown)

physicslightspeedRelativityvacuum