Rag - a large, square piece of fabric, net, vinyl or other materials with grommets in a sturdy, sewn edge. Rags are usually tied to an equal sized open frame using trick line or shoelace from grommets to frame. 6X6 and 12x12 foot sets are common, with larger sizes available. A basic set would include a solid black/white griffolyn (which can bounce or flag, a single and a double net and a silk. Light tension is required for wrinkle-free mounting, but rags shouldn't be stretched too tightly - they can be easily damaged. They can be rigged between "found" objects, and used "loose" or unmounted. Rags can be silks, single and double nets, reflectors (silver or gold lame'), vinyl bounce materials (black, white and checkerboard) and more. Used outdoors, rags must be safety-rigged to stationary objects and sandbagged as well. Rags easily become sails or kites even in mere breezes, and can wreak serious damage if they get loose or fall over. Tie and bag them down!
Rectifier - an electronic device for converting alternating current (AC) to direct current (DC).
Redhead - is a nickname for an open-faced 1K light, a.k.a. "a mickey".
Reflector - refers to any piece of gear with a surface designed to reflect light (obviously). The standard reflector used in video/film production is also known as a "shiny board", and has a yoke or open end rectangular frame with a junior stud. The frame has pivots which allow tilting/positioning of the beam reflected for easier aiming, and a lock knob to keep in from moving once aimed. Reflectors can have a smooth reflective covering, or a broken up reflective surface, composed of small squares of reflective material with loose edges, thus softening the beam of light reflected. Some reflectors are actually mirrors. They are much heavier than a standard reflector, but they can really kick out an intense beam. Standard foil or mylar surface reflectors are usually bright enough, however, and mirror reflectors aren't seen too often. Another variation in reflective surface is gold-tinted foil, which gives a warmer light beam. Large frame type "rags" can have refective surfaces, too, for a really large but softer beam, such as a 12x12 silver or gold lame'.
Rigging - describes several types of activity as well as equipment on film sets. Laying out power lines to lights and other electrical needs can be referred to as rigging. More often, rigging means setting up and securing special camera mounts, analog and mechanical special effects, light grids (studio) or trusses (location/peformance), platforms, supports, sound baffles, larger practical props and what ever else might need to be assembled, hung, tied off, etc. Example: "Hey, Grips... rig a safety line to that 12 by frame!".
Rim (lighting) - is a backlight positioned more directly behind the subject than a kicker (positioned slightly to the side and above the subject) or normal backlight (higher positioning above and behind the subject). It creates a hard rim of light equally on all edges of the subject, a white outline effect, depending on intesity of the rim light and any other modeling lights in play on the shot..
Riser - in grip/lighting terms, a platform to raise lights, crew, set pieces or cameras, tripods and more. Risers can also be the telescoping sections of a light or c-stand - i.e. "2-riser", "3-riser", etc. In camera equipment terms, a riser is a device placed between the camera mount and a dolly mount or other mount to add height to the camera.
Roller - any grip/ or light stand that has wheels. The height capability or number of telescoping sections will determine the name, such as high-rollers, etc. Most roller type light and support stands have junior receivers, since they tend to be used for heaver film production lights and frames with corresponding mounts. Most stand wheels have solid metal hubs with rubber strips, while a few may have inflated wheels for rolling over sand, dirt and rougher surfaces.
Rolling - is called out when film, tape or even digital media is recording ("we're rolling"). Basically means recording of souind or image capture functions are engaged. Usually followed by a call of "speed" when rolling is definite and a bit of lead room has been laid down before "action" is called .
Rough in - the initial approximate placement of lights for a shot or scene. The layout is then adjusted or "polished" per the LD, Gaffers' or DPs' instructions. Sometimes a grip and lighting crew jumps ahead of the currently shooting lit scene and roughs-in the lights and gear for the next set, scene or location.