Relative refractive index (n) is the ratio of the speed of light in a vacuum relative to that in a given material or medium. It is a measure of how much a material or medium slows down light when it passes through it. It is also known as the refractive index of the material or medium.
Absolute refractive index is the ratio of the speed of light in a vacuum relative to that in a vacuum. It is a measure of how much a material or medium can slow down light when it passes through it. It is also known as the absolute refractive index of the material or medium.