Final answer:
A spectrum is a graph that shows either a continuous range of colors or specific wavelengths absorbed by a substance, plotted against the wavelength of incident light.
Step-by-step explanation:
The plot of absorption spectrum against the wavelength of incident light is called a spectrum. A spectrum can show a continuous range of colors or it could be a series of discrete lines known as a line spectrum. When light from artificial sources is passed through gases, absorption spectra with dark lines are seen, which represents specific wavelengths being absorbed by the gas. Spectra are also produced when sunlight is dispersed by a prism, revealing its continuous spectrum of colors. This continuous distribution of colors represents different wavelengths from ultraviolet (shorter wavelengths) to infrared (longer wavelengths), which are invisible to the human eye but can be detected with instruments.