The Nikkei 225 marked the peak of Japan's late-1980s asset bubble at 38,915.87.
The index reached that closing level on December 29, 1989, after a spectacular rise in Japanese share and property prices. Easy credit, optimistic expectations, and strong asset demand helped push valuations to extraordinary levels during the bubble.
Prices then reversed. The Nikkei fell sharply during the early 1990s, while Japan entered a prolonged period of weak growth, banking problems, and deflationary pressure. The market collapse is often associated with Japan's “lost decades,” although that phrase covers a complex economic history.
The cited figure is the Nikkei 225's closing peak, not a property-price measure or an intraday record. The index did not return to that closing level for decades.