The phenomenon of the splitting up of white light into its component colours is called
dispersion
White light is composed of seven colours red, orange, yellow, green, blue, indigo, and violet (VIBGYOR). Dispersion is the property by which light is spread out according to its colour as it passes through an object. For example, when white light falls into water droplets, all of the different colours present in sunlight bends by different amounts, so they spread out and make a rainbow.