If something is biodegradable, living things — mostly bacteria and fungi — can break it down into simpler stuff that does not sit in the ground or the sea for hundreds of years. People say it about bags, forks, packaging, and some chemicals. It is a science-and-shopping word; in everyday talk you might just say “it will rot” or “it can break down”. Though actually, the word is used more loosely than the tidy meaning. A “biodegradable” plastic may only break down in a hot industrial compost machine, not in your garden and not in the ocean. Companies like the label because it sounds kind. A careful speaker asks: biodegradable where, and how fast? Something can be biodegradable and still make a mess if it is thrown in the wrong place.