The angle of refraction refers to the angle between a refracted ray and a line perpendicular to the surface it enters. It occurs when light passes from one medium into another, causing its direction to change.
Snell's law describes how light bends or refracts as it passes through different mediums. It states that 'the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.'
The refractive index is a measure that indicates how much light slows down or speeds up when passing through different materials. It quantifies how much light bends as it enters a new medium.