Gaffer (1): Chief electrician on a film set. More info: Film Gaffer
Gaffer (2): Industrial-strength sticky tape, AKA duct tape.
Gauss: (pronounced "gows", abbreviation "G") Unit of magnetic induction.
Gel: (pronounced "jel") Semi-transparent heat-resistant material which is placed in front of a light source in order to modify it's colour temperature or other characteristics. Related info: Color Temperature
Geosynchronous: A satellite orbit in which the satellite remains in a fixed position above the Earth.
Graphic Equalizer: A type of audio equalizer which uses a graphical layout to represent the changes made to various frequencies. More info: Graphic Equalisers, Sound Equalization
Gray Card: A gray-coloured card which reflects a known, uniform amount of the light which falls upon it. Used as a reference to calibrate light meters and set exposure. More Info: Grayscale Chart, 18% Gray Card
Gray Noise: Random noise, similar to white noise, which has been filtered to make all frequencies appear equally loud to the human ear. More info: Gray noise, Noise colors
Green Noise: An unofficial term referring to the background ambient noise of the world. Can also mean the mid-frequencies of white noise. More info: Green noise, Noise colors
Green Room: A room located near the main stage in a studio or concert venue, where artists and guests wait before their appearance. More info: Green room
Green Screen: A film and video technique in which action is shot against a green screen, which is subsequently removed from the image and replaced with a different background. More info: Green Screen , Chroma Key
Grip: Person who is responsible for constructing and dismantling film sets, as well as laying down dolly tracks.