Light is deviated from its straight ahead/line path when it passes through a tiny slit, tiny hole, or very near a sharp edge. The process by which this takes place is called diffraction. ‘Tiny’ means a slit or hole that is about equal to the wavelength of the light. Following its passage through such a small slit or hole, or near a sharp edge, white light is dispersed into a rainbow of colours. That dispersion of light is called the diffraction pattern.