The index commonly known as the Nikkei during Japan’s asset-price crash was the Nikkei 225.
The Nikkei 225 is a price-weighted index of 225 major companies listed on the Tokyo Stock Exchange’s Prime Market. It is Japan’s most widely recognized stock-market benchmark and is frequently used in accounts of the collapse of Japan’s late-1980s asset bubble.
The index reached an all-time closing high of 38,915.87 on 29 December 1989. After the bubble burst, Japanese share and land prices fell for years. The prolonged economic stagnation became associated with Japan’s “lost decades.”
The Nikkei 225 is not the same as TOPIX. TOPIX is a broader, capitalization-weighted index covering companies listed on the Tokyo Stock Exchange’s main market structure. Both are important, but historical crash headlines often cite the Nikkei.