Refractive index is a fundamental property of a material that describes how much light is bent or refracted as it passes through the material. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the material. Refractive index is an important parameter in optics, photonics, and materials science, as it determines how light is transmitted, reflected, and absorbed by a material. Researchers study refractive index to understand the optical properties of materials, develop new optical devices and technologies, and design materials with specific optical characteristics.