Nikkei

What Does Nikkei Mean?
Short for Japan's Nikkei 225 Stock Average, the leading and most-respected index of Japanese stocks. It is a price-weighted index comprised of Japan's top 225 blue-chip companies on the Tokyo Stock Exchange. The Nikkei is equivalent to the Dow Jones Industrial Average Index in the U.S. In fact, it was called the Nikkei Dow Jones Stock Average from 1975 to 1985.

Investopedia explains Nikkei
The index has been calculated since Sept 1950 (retroactively since to May 1949). A few years after the country's leading business newspaper the Nihon Keizai Shimbun (Nikkei or Japan Economic Daily) began to commission the calculations, it was renamed.