1. Having a high photographic speed. The term may be applied to a photographic process as a whole, or it may refer to any element in the process, such as the optical system, emulsion, developer.
2. Resistant to the action of destructive agents. For example, a dye image may be ‘fast’ to light, fast to heat, or fast to diffusion.
1997, Student Filmmaker’s Handbook, 4th Sprl edition, Eastman Kodak Company, Rochester, New York.