"The index of refraction is a measure of how much a light ray bends when it passes from one medium into another."

Here's why:

* Index of refraction: This is a specific term that refers to the ratio of the speed of light in a vacuum to the speed of light in a given medium. It quantifies how much the light slows down as it enters a denser medium.

* Refraction: This is the bending of light as it passes from one medium to another. This bending occurs because the speed of light changes as it transitions between mediums.

The higher the index of refraction, the more the light bends. For example, light bends more when it goes from air into water (high index of refraction) than when it goes from air into glass (lower index of refraction).