What does the term ‘refraction’ describe in optics?

The term 'refraction' in optics specifically refers to the bending of light as it passes from one medium to another, which has a different density. This bending occurs due to the change in speed of light as it enters a new medium—like air to water or glass. The degree of bending is described by Snell's Law, which quantifies how light behaves at the interface of two media. When light transitions from, for example, air into glass, it slows down, leading to a change in direction or bending of the light rays.

This phenomenon is fundamental in understanding how lenses work, as it is the refraction of light that allows lenses to focus or disperse light beams. The other options, while related to optics, do not accurately capture the essence of refraction. Reflection describes the bouncing of light off surfaces, color dispersion pertains to the separation of light into its component colors (as seen in prisms), and curvature measurement of a lens relates to its physical shape but does not encompass the action of bending light. Therefore, the correct answer clearly identifies the core concept of refraction in optics.