大起大落 is a four-character set phrase (成语) that describes extreme, rapid fluctuations — usually in prices, fortunes, emotions, or career paths. The literal meaning is 'big rise, big fall'; you can use it for stock markets, a person's life story, or any situation that swings wildly between highs and lows. Unlike the verb phrase tag might suggest, it functions more like an adjective or an idiomatic expression describing a volatile state.