The phenomenon of splitting up of white light into its constituent colours on passing through a prism is called dispersion of light.
A prism is made up of a transparent medium bounded by two plane surfaces inclined at an angle.
it consists of two plane reflecting surfaces. when white light it is incident on one reflecting surface of the prism, the yellow light splits up into consistent colours - violet, Indigo, blue ,green ,yellow, orange and red.
the band of colours obtained is called spectrum of light. The spectrum of light(VIBGYOR) can be seen on a screen placed on the other side of the prism.