When a wound festers, it becomes infected and fills with pus instead of healing properly. If you get a splinter and don't remove it, the area around it might start to fester: it gets red, swollen, and painful as bacteria multiply in the wound.

The word also describes problems or bad feelings that get worse over time when ignored. When two friends have an argument and refuse to talk about it, their hurt feelings might fester, growing into real anger or resentment. A small disagreement that could have been resolved with an honest conversation can fester into a serious conflict when left alone.

You might say that jealousy can fester, or that complaints fester in an organization where nobody listens to problems. Just like an untreated wound, these situations don't improve on their own: they need attention and care to heal. The image is powerful because it reminds us that ignoring problems, whether physical or emotional, can make them worse, not better.