In film, television or video production, craft service refers to the department which provides food service and beverages to the other departments or crafts. In addition to policing the set, they provide buffet style snacks and drinks. The crafts in film refers to departments such as camera, sound, electricians, grips, props, art director, set decorator, special effects, hair and make-up, background.
There is a difference between craft service and catering. Craft service is the food that is always available to the crew while they are working, and can range from a single table of cookies, candy, cereal and coffee (on a low-budget indie feature), to more elaborate meals. Catering handles the true meals like lunch (which, on most American shoots, occurs six hours after the start of the day's filming, even if that means 2 a.m.) and second meal (which occurs six hours later, if the crew has not finished the day's work).
Catering is a sit-down hot meal that lasts either 30 minutes or an hour, unless the crew is working "French hours" (also called "Northwest hours" in Seattle and Vancouver), in which case the meal is brought to the set, and people eat whenever they get a chance.
Craft service is a crew position and craft service people are sometimes represented by the union, the International Alliance of Theatrical Stage Employees (IATSE). In Los Angeles craft service workers are represented by IATSE Local 80.
In the mid-1920s to the late 1940s, the International Alliance of Theatrical Stage Employees and Motion Picture Machine Operators organized the motion picture and television production business in Hollywood. Locals represented set lighting technicians, grips, cameramen, prop-makers, make-up artists, and many others. The idea was to create better working conditions and pay.
As the technology evolved, crew positions became more specialized, and "crafts" could no longer cross over, for example, electricians doing "grip work" by moving a stand. It became necessary to hire an "all-around" laborer who could help any department and perform menial tasks such as digging holes or cleaning up after animals. These laborers could be temporarily upgraded in salary. They could be put on the "cable rate" for helping to guide sound or lighting cables for a shot.