Regular reflection, also known as specular reflection, occurs when light rays are reflected from a smooth, flat surface at the same angle as they hit the surface. This type of reflection produces a mirror-like effect, where the reflected light forms a distinct image of the source.

Diffused reflection, on the other hand, occurs when light rays are scattered in many directions upon hitting a rough or uneven surface. This type of reflection does not produce a clear image, as the reflected light is spread out and dispersed in all directions.

The surface of a pond is typically not smooth and flat, but rather rough and uneven due to the presence of ripples, waves, and other irregularities. As a result, when light hits the surface of a pond, it undergoes diffused reflection. The reflected light is scattered in all directions, creating a uniform distribution of light intensity over the surface of the pond. This diffused reflection is what gives the surface of a pond its characteristic shimmering appearance.