Absorption and Emission Spectra

"White" light is an example of a continuous spectra, in that it consists of light of every wavelength.  Heated gases of elements, on the other hand, emit light only at specific wavelengths.  Each element has it's own characteristic emission spectrum.  Conversely, cold gases of elements absorb light at specific wavelengths.  By passing white light through a cold gas, you can obtain an absorption spectrum.

Absorption and Emission Spectra Java Applet
Periodic Table of the elements that displays the emission and absorption spectra for almost every element

Absorption Spectrum for the Sun