In cinema, butterfly is a methodology of lighting sets. When controlling light, grips use a variety of flags (black, opaque material), nets (one, two, or three layers of black, white, or semi translucent bobinette), and diffusion (translucent white materials of different densities). Generally, these are sewn onto frames of standard sizes, which are kept in racks or on carts where they are easily accessible. However, when a flag, net, or diffusion is needed to cover a larger area it is not practical to keep it built and sewn on the truck; thus, Butterflies.
Butterflies are also known as overheads, or are simply called for by their dimensions, which are standard: 6 ft. x 6 ft, 8x8, 12x12, and 20x20 are the standard nominal, or frame sizes, the material, often referred to as "rags", or Goods, tend to finish at about 8 inches less on a side in order to assure a flat, stretched surface. Further, while the standard rags mentioned above are on every grip truck, butterflies are often rigged with reflective fabrics as well, for instance, silver lame.