Refraction and reflection refer to the behavior that occurs when a wave; e.g. light, sound, or seismic, encounters a material with different physical properties than what it was traveling in. For instance, light traveling through the air moves at a certain speed and in a certain direction. However, when it encounters another material, say water, some of the light can bounce off the water surface. This is called reflection, and follows the law that the angle of reflection will equal the angle of incidence on the surface (measured from the normal to the surface). So, if the light comes in at an incidence angle of 45 degrees it will be reflected at 45 degrees.
In the case of light hitting water, some of the light will not be reflected, but instead will pass into the water. The speed of light in water is slower than the speed of light in air, so the light ray slows down. This results in the light bending slightly, an effect known as refraction. Refraction follows Snell's law which states: n
1sin(angle of incidence) = n
2sin(angle of refraction), again measured from the normal to the interface. The quantity n, or index of refraction, is defined as n = c/(velocity in the medium), where c is the speed of light in a vacuum and the denominator is the speed of light in the medium, in this case water. This is what causes things to look bent when they pass from air into water. Sound, and other important waves have the same properties as light waves for reflection and refraction.
