1. Refraction: This occurs when a wave passes from one medium to another, causing it to bend. The speed of the wave changes as it enters the new medium, leading to a change in direction. A common example is light entering water from air, causing it to bend towards the normal (an imaginary line perpendicular to the surface).

2. Diffraction: This happens when a wave encounters an obstacle or opening. The wave bends around the edges of the obstacle, spreading out as it passes through the opening. This is why you can still hear sound around corners, even though you can't see the source directly.

3. Reflection: When a wave hits a barrier, it bounces back. The angle of incidence (the angle at which the wave hits the barrier) is equal to the angle of reflection (the angle at which the wave bounces back). Mirrors reflect light waves, while echoes are caused by sound waves reflecting off surfaces.