The Nikkei 225 is the most important stock index in Japan. It reflects the country's business activity and includes 225 stocks from various companies that are traded on the Japanese Stock Exchange. The index itself displays the arithmetic average of these stocks' values. It was introduced on September 7, 1950, and its value was first published on that date. The index was named after the publication that computed it.
https://en.wikipedia.org/wiki/Nikkei_225

The NIKKEI 225 is a leading stock market index representing the performance of 225 prominent companies listed on the Tokyo Stock Exchange (TSE). Established in 1950, it serves as a barometer of Japan's economic health and one of Asia’s most significant market indicators.

Unlike market-cap-weighted indices, the NIKKEI 225 is price-weighted, meaning companies with higher stock prices have a greater influence on the index’s movement, regardless of their size. It spans various sectors, including technology, automotive, and finance, featuring global giants like Toyota, Sony, and SoftBank.

The index is widely tracked by investors globally due to Japan's role as a major economy. Its performance reflects investor sentiment, economic trends, and geopolitical factors impacting the region.