Reflection of light is when light bounces off an object. If the surface is smooth and shiny, like glass, water or polished metal, the light will reflect at the same angle as it hit the surface. This is called specular reflection. Diffuse reflection is when light hits an object and reflects in lots of different directions. This happens when the surface is rough.
The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray. The reflected ray is always in the plane defined by the incident ray and the normal to the surface