When discussing light,  a spectrum is a linear scale of spectral colours organised by wavelength.


A spectrum or spectra (plural) are produced naturally when light is refracted by a prism or by rain.

A diagram of spectral colours is usually presented in the form of a spectrum, a linear band organised by wavelength with red at one end and violet at the other.

Spectra are often shown in an elongated form so that as many different gradations of colour can be seen as possible.