1) Japanese market index 2) Japanese stock average 
The common term for the Nihon Keizai newspaper, Japan`s leading financial newspaper. The Nikkei usually refers to the price-weighted average of 225 stocks of the first section of the Tokyo Stock Exchange.
The index of the 225 leading stocks that are traded on the Tokyo Stock ExchangeA price-weighted index
an index showing the average closing prices of 225 stocks on the Tokyo Stock Exchange. · an American of Japanese descent.