The prolonged Japanese economic downturn after Japan’s late-1980s asset bubble burst is known as the Lost Decade.
Japan’s stock and real-estate prices rose dramatically during the second half of the 1980s. The Nikkei 225 reached an all-time closing high of 38,915.87 on 29 December 1989. After the bubble burst, equity and property values declined sharply, weakening banks, businesses, and household balance sheets.
The phrase originally described the 1990s, when Japan experienced sluggish growth, falling prices, financial-sector stress, and repeated periods of recession. Some economists later extended the label to cover the difficult years of the 2000s, calling that longer period the “Lost Decades.”
The Lost Decade is therefore not the formal name of one trading day or one exchange crash. It refers to the wider economic aftermath of the asset-price collapse, while Japan’s stock-market fall was one of its most visible beginnings.