Source : Webster's Revised Unabridged Dictionary (1913)

Diffraction \Dif*frac"tion\, n. [Cf. F. diffraction.] (Opt.)
   The deflection and decomposition of light in passing by the
   edges of opaque bodies or through narrow slits, causing the
   appearance of parallel bands or fringes of prismatic colors,
   as by the action of a grating of fine lines or bars.

         Remarked by Grimaldi (1665), and referred by him to a
         property of light which he called diffraction.
                                                  --Whewell.

   {Diffraction grating}. (Optics) See under {Grating}.

   {Diffraction spectrum}. (Optics) See under {Spectrum}.

Source : WordNet®

diffraction grating
     n : optical device consisting of a surface with many parallel
         grooves in it; disperses a beam of light (or other
         electromagnetic radiation) into its wavelengths to
         produce its spectrum [syn: {grating}]