Question

what is meant by refractive index

Answer 1

refractive index is the ratio of the velocity of light in a vacuum to its velocity in a specified medium.
hope this will help u
pls Mark as brainlist

Answer 2

absolute refractive index is defined as a ratio of the speed of light in the vacuum and in selected medium  

relative refractive index is defined as a ratio of speed of light in two different media

When in relative refrective index ,second medium is vacuum then both will be same

Formula n=c/v