What is "bipack"

n. (context cinematography English) The process of loading two reels of film into a camera, so that they both pass through the camera gate together, formerly used for visual effects and as a subtractive colour process.

In cinematography, bipacking, or a bipack, is the process of loading two reels of film into a camera, so that they both pass through the camera gate together. It was used both for in-camera effects (effects that are nowadays mainly achieved via optical printing) and as an early subtractive colour process.