Moobs are the soft, rounded bits on a man’s chest that look like breasts. They may be fat, or muscle that sits in a breast-like shape. The word is informal, jokey, and often unkind — tabloids, gym talk, and the internet use it; you would not say it in a polite or formal setting. It is not a doctor’s word. A doctor might talk about extra chest fat or, in some cases, a real swelling of breast tissue; moobs is the teasing everyday label, and it can hurt. People also say man boobs, which is the same idea in two words.