Short for “go between.”
2. A metal, wood, or fabric panel or sheet that is placed in front of a light source to produce a particular shape or pattern to the light beam that is cast out. This is done using slots, holes, and shapes cut out of the gobo material to allow light to pass, while other areas of the light beam are blocked, creating shadows.
In modern theatrical or movie production, gobos are often referred to as “flags,” and are generally black fabric with a pattern cut out that is stretched over a steel frame and placed in front of a projector or light.