The coloured band obtained on a screen after passing white light through a prism is called the spectrum. Bending is least for the red colour and maximum for violet colour.
In the Newton's experiment showing recombination of light, if the second prism is kept upright i.e same as that of the first prism then a widely seperated band of seven colours will be formed in the same order. All the colours will get refracted towards the base of the prism. On the other hand when he turned the second prism in such a way that the refracting surfaces are parallel to each other, the seperate bands formed combined to form white light again.