> Apart from in relativity, the most pervasive use of c to represent a speed today is in the wave equation This gives credence to what I was taught since high

> Apart from in relativity, the most pervasive use of c to represent a speed today is in the wave equation This gives credence to what I was taught since high school, in French physics class: v=vitesse (speed), c=célérité (celerity). Speed is used when talking about physical object movement, celerity is used when talking about propagation of a phenomenon (wave speed). https://fr.wikipedia.org/wiki/C%C3%A9l%C3%A9rit%C3%A9 https://fr.wikipedia.org/wiki/C%C3%A9l%C3%A9rit%C3%A9 Though since c has come to specifically mean the speed of light is a vacuum as a notation, I see it used less often for other wave speeds when the constant is needed. Both speed and celerity are still used when writing and talking, with their respective meanings.