What does refraction describe?

Refraction describes the change in the speed of a wave as it passes from one medium to another. This change in speed leads to a change in the direction of the wave, which is notably observed with light waves when they travel through different materials, such as from air into water or glass. When light enters a new medium at an angle, the difference in density between the media causes the light to change its speed and bend. This principle is fundamental in explaining various optical phenomena and is utilized in the design of lenses and prisms, among other optical devices.

The other options describe distinct physical phenomena: scattering involves disruption and redirection of light in multiple directions due to encounters with small particles, reflection refers to the bouncing back of waves from surfaces, and standing waves result from the interference of waves in a particular medium, which is a different concept entirely. Each of these describes different behaviors of waves under various conditions and does not relate to the specific process of refraction.