Question

why not velocity of light why speed of light.

Answer 1

Because velocity is directional in nature but speed not.
Light move non directionally because of refraction of light.
Due to refraction of light light bent in many directions i think you understand it well

Answer 2

Heya user!!

We know that velocity has direction (speed of a body in a given direction).But speed means rapidity.Speed is the magnitude of velocity and it has no direction!!

But in the case of light...when it takes birth from a point it travels in to diff direction.But it can also change it's path and can be curved as someone has already told you below!!

So we use velocity instead of speed
☺☺Hope it helps☺☺