The bending of light, sound or heat waves is known as refraction. Refraction occurs when a light wave, heat wave or sound wave moves from one medium to another.
When a wave travels from one medium to another with a different density, the velocity of the wave changes. This change in velocity changes the direction of the wave, making it bend. The bend occurs at the interface, the point at which the medium changes. Though the velocity changes, the frequency of the wave remains constant. The change in direction can be calculated using Snell's law and is frequently used in optics development.