Outdated Stock definition
Since film is perishable, dyes will change color and the grain will build up over time. The end result is an image that contains less and a foggy appearance. Even if film is refrigerated, the effects of time will take their effect after 2-3 years. Slow films tend to grow foggy in a longer amount of time than faster films. And black and white film lasts a little while longer in quality than color film. However, if one is trying to save a buck or two and does not need the longevity, outdated stock can be bought inexpensively.