Topix
In short
The Tokyo Stock Price Index tracks the performance of a wide range of companies listed on the Tokyo Stock Exchange. It serves as a broad measure of the Japanese stock market alongside the Nikkei 225.
In plain words
It is a list used to see if the Japanese stock market is going up or down. Unlike other lists that only look at big names, this one looks at almost all major companies in Japan.
A simple example
If most large companies in Tokyo see their share prices rise, the TOPIX value will increase. This tells investors that the overall Japanese economy is doing well.
Why it matters
It provides a more complete picture of the Japanese economy than indices that only track a few large firms. Many professional investors use it to judge market trends.
Easy to mix up
Do not confuse it with the Nikkei 225, which only tracks 225 specific large companies.