Things that have gotten damp and started to smell musty can be described as moldy. You can also use this word for things that are actually growing a fungus on them, like your bag of moldy bread.
Mold is a particular type of fungus, often greenish or gray in color. Things become moldy from being stored in dark, damp places or in the case of some food, from not being refrigerated. If you wait months to clean out your locker and throw away your old lunch bags, you might find mold growing on bread crusts, yogurt, or containers of leftover ravioli. Ditch those moldy remnants!