What is refractive index? Expert please anwer it..

The refractive index is the ratio of the speed of light in a given medium which gives a mesure of extent of refraction as it travels from one medium to another medium

There are two types of refractive index?
(1) Relative refractive index- the rationof a speed of light in a given two mediums i.e. refractive index of medium 2 with respect to medium1
(2) Absolute refractive index- the ratio of a speed of light in a given medium with respect to the vaccum