Regular reflection occurs when light bounces off a smooth, polished surface in a predictable, orderly manner, while irregular (diffuse) reflection occurs when light bounces off a rough or uneven surface in many random directions.
With regular reflection, parallel rays of light remain parallel after bouncing, creating a clear image. This happens because the microscopic bumps on the surface are smaller than the wavelength of light, so the surface acts as a single, uniform mirror. Examples include reflections in still water, polished metal, or a mirror.
With irregular reflection, parallel rays scatter in different directions because the surface has many small slopes and irregularities. Even though each ray still follows the law of reflection (angle of incidence equals angle of reflection), the uneven surface causes the reflected rays to diverge. Examples include light bouncing off paper, fabric, concrete, or a painted wall.
This distinction is important because regular reflection preserves the image of an object, while irregular reflection diffuses the light, which is why you can see yourself in a mirror but not in a crumpled piece of paper. Most objects around you produce irregular reflection, which is actually why we can see them from different angles—light scatters in all directions rather than bouncing back along a single path. The quality of reflection depends on the surface smoothness relative to the wavelength of light being reflected.