When food rots, it decays and breaks down until it becomes disgusting and unsafe to eat. A rotten apple turns brown and mushy, smelling sour and awful. Rotten eggs release a terrible sulfur smell that makes people gag. Bacteria and mold cause this process, feeding on the food and changing it into something completely different from what it was. That's why you keep food in the refrigerator: cold temperatures slow down rotting.

The word also describes things that are corrupt, unfair, or morally wrong. A rotten deal means someone's being cheated. When a story has a villain who seems charming but turns out to be cruel, you might say they're “rotten to the core,” meaning bad all the way through, not just on the surface.

People sometimes use rotten to describe feeling sick (“I feel rotten today”) or to describe something of poor quality. A rotten performance means someone did a terrible job. When your day goes badly from start to finish, you might call it a rotten day.

Interestingly, spoiled means nearly the same thing as rotten when talking about food, but calling a person spoiled means something different: they're used to getting everything they want and behave badly because of it.