A Gobo is a thin metal disc used to create patterns or designs of projected light.  The name comes from the term “Goes Before Optics” meaning the scrim goes “in between” the light source and the projected area.   Gobos are similar to a Cucoloris or Flags, except that the Gobo is actually mounted onto the light or lamp itself, whereas Kooks & Flags are placed further away from the intense heat of the lamp.  (Also see Cucoloris and Scrim.)