Feeling restless, jumpy and a bit mad because you have been shut inside one place too long. It is not real madness — it is the itchy, can't-sit-still feeling you get on day five of staying home, when you start talking to the wall or reorganising a drawer for no reason. The word came out of prison slang, but almost nobody uses it about prison now. People use it about being stuck at home: sick in bed, snowed in, in quarantine, on a long flight, in hospital, or minding small children in a small flat. It is informal and friendly, and there is usually a bit of a joke in it — you say it about yourself, or to a friend, not in a report or an essay. It almost always comes after the verb be or go: 'I'm going stir-crazy.' 'Go' is the most common, because the word is about the change, the slow turn from fine to not-fine. You can also say someone is stir-crazy after too long inside. Note the hyphen; both parts are stressed.