The wave interaction you are describing, where a wave bends as it passes from one medium to another at an angle, is known as refraction. Refraction occurs because of the change in speed of the wave as it moves between different media. This is the principle that causes the bending of light waves, such as when light passes through a prism to create a rainbow.
- Diffraction is the bending of waves around obstacles and openings.
- Reflection is the bouncing back of waves when they encounter a surface.
In your context, the correct term is refraction.