What does the term "refraction" refer to in optics?

The term "refraction" in optics specifically refers to the bending of light as it passes from one medium to another, such as from air into water or through a lens. This bending occurs due to a change in the speed of light as it crosses into a different medium, which alters its direction. Understanding refraction is crucial in various applications like lens design, eyeglasses, and optical instruments, as it affects how we perceive images and how light behaves when interacting with different materials.

The other options relate to different concepts: measuring distance pertains to spatial analysis, calculating angles involves geometric principles, and enhancing brightness relates to the intensity of light rather than its behavior. Each of these concepts is distinct from the fundamental phenomena described by refraction.