"Moldy bread" refers to bread that has become contaminated with mold, a type of fungus. It is usually not safe to consume, as the mold can cause health problems. Full definition
The bulge of what looks to be upward of 50 faces is interspersed with printed and diced «hair» — which spurts out between the faces like seaweed — and is then surrealistically sprinkled with replicas of moldy bread slices (which are also printed and formed in the same manner.) (observer.com)
Aware this is written in jest, but eating moldy bread could make you sick. (bonappetit.com)
Moldy bread gets trimmed and pulverized into breadcrumbs. (treehugger.com)