The Nikkei 225, or simply the "Nikkei", is the premier index for the stock market in Japan, similar to the Dow Jones Industrial Average for the New York Stock Exchange. As of mid-2017, the value of the Nikkei hovered around 20,000.
As its name indicates, the Nikkei 225 is compromised of 225 of the leading Japanese stocks. Its composition is reviewed at least annually and its components are adjusted accordingly.
Unlike the DJIA and other premier American indexes, the Nikkei 225 does not tend to increase steadily over time. For example, on January 1, 1990, the Nikkei was worth more than 37,000 - nearly double what it is worth in 2017.