Moldy is the American spelling of British mouldy. If something is moldy, the fuzzy growth — mold — has grown on it. Bread, cheese, fruit, walls in a wet room. You throw moldy food away, except some cheeses, where the mold is put there on purpose and is safe to eat. People also stretch the word when there is no real fungus: a moldy old joke, a moldy smell in a basement, meaning stale, old, and a bit unpleasant. That stretch is informal and a little disgusted, but it is not a rude word. Mold is the stuff itself; moldy describes the thing that has it. “Moldy bread” is the usual pair.

美式拼法（英式 mouldy），發霉的