If continuous spectrum light from a star passes through a cool, low-density gas on its way to your telescope and spectroscope, spectrum on the continuous spectrum results

a dark (absorption) line

Explanation:

If a continuous spectra light is passed form the star and it cools down through a low density of star having a low density of gas on its way to the telescopes and spectroscopes. The presence of a continuous dark spectrum of absorption of light will be the result of this. They refer to the narrow intensity that is the result of the photons being absorbed that pass through.