Colored sheets of transparent plastic (able to withstand high temperatures) that are applied to lights and windows to change the intensity or the color of the light. 
Gel Frame – A square metal frame that has a “pin” on one side in order for it to be mounted or attached to a C-Stand or Gobo Arm.  The Gel Frame is used when a Gel is needed to alter the color or the quality of light emanating from a Movie Light (or Lamp).  The “Frame” holds the Gel tightly in place with either “C-47’s” or with “double-stick” tape.