Light bends as its speed changes when the light beam crosses the boundary from one material into the next. When light bends, it is called refraction. The direction it bends is determined by the speed at which it crosses the boundary.
When a person holds a stick in a pond and the stick appears to bend, that is because the light is refracted on the surface of the pond. The light bends and gives the illusion that the stick is bending, or is at an angle.
The density of the material through which the light passes determines the speed of the light. If light is traveling from a less dense material into a one that is more dense, then it will slow down. This causes the light beam to be refracted in an upward direction. This is referred to as "toward normal." However, as a light beam travels from a more dense material into one that is less dense, it moves faster. The light is then refracted in the opposite direction, or downward. This is referred to as the light bending "away from normal."
Usually, the bending of light has some type of external cause such as the stick in the pond. However, in 2012, physicists at the Israel Institute of Technology were working on a method where light could bend by itself. This could be useful in optical tweezers and burning a curved hole through an object.