Dispersion of white light is defined as the splitting of white light into seven constituent colors when passed through the prism.
When white light is passed through a glass prism it splits into its spectrum of colors (violet, indigo, blue, green, yellow, orange and red) and this process of white light splitting into its constituent colors is termed as dispersion.
When white light is made to pass through a prism, a spectrum of seven colors is formed which shows that white light is a mixture of seven different colors. Prism only acts as a medium for the separation of the seven colors.
The acronym VIBGYOR (Violet-Indigo-Blue-Green-Yellow-Orange-Red) is a popular mnemonic device for remembering the spectrum of light.
Hence, the white light is composed of seven different colors namely (violet, indigo, blue, green, yellow, orange, and red).