The term GROWTH ON OLD BREAD can be summarized as the development of mold on bread that has been left out for a period of time. Mold is a type of fungus that can grow on food, and it is usually visible as a green or black spot on the surface of the food. Mold can cause food to spoil and become inedible, so it is important to store bread properly and consume it before it has a chance to develop mold.