A gaffer in the motion picture industry and on a television crew is the head electrician, responsible for the execution (and sometimes the design) of the lighting plan for a production. The term gaffer originally related to the moving of overhead equipment to control lighting levels using a gaff. The gaffer's assistant is the best boy.
Sometimes the Gaffer is credited as Chief Lighting Technician (CLT).
The Gaffer is responsible for managing lighting, including associated resources such as labour, lighting instruments and electrical equipment under the direction of the Director of Photography (the DP or DOP) or, in television, the Lighting Director (LD).
The DP/LD is responsible for the overall lighting design, but delegates the implementation of the design to the Gaffer and the Key Grip. The Key Grip is the head grip, in charge of the labour and non-electrical equipment used to support and modify the lighting. Grip equipment includes stands, flags and gobos. The Gaffer will usually have an assistant called a best boy and, depending on the size of the job, crew members who are called "set lighting technicians" or "electricians", although not all of them are trained as electricians in the usual sense of the term.
Although gaffer tape is used within the film/TV Industry as a strong cloth-backed adhesive tape, many other types of tape are also used, such as paper tape, pressure-sensitive tape (A.K.A. snot tape), electrical tape, J-LAR, and cloth tape. Gaffer tape is typically utilized by set lighting technicians under the supervision of, and not directly by, a Gaffer.