Some molds, like water molds, live on the bodies of dead insects and other animals in the water. Others are parasites, invading the tissue of living animals. Several species of Penicillium have economic value. Some are used in cheesemaking, in which enzymes secreted by the mold give the cheese its flavor. Mold is growing on bread that was left in a warm, dark, damp place.
Molds are the common name for a group of fungi which often have threadlike filaments, called hyphae.
An Introduction to the Fungi, 3d ed.