Stock index refers to the quantity or value of a specific commodity, service or other resource at a specific point in time. The stock index is usually opposite to the flow index, which refers to the trading volume or trading speed in a certain period of time. For example, a country's GDP is the total value of its economy at a certain point, which is a typical stock index. Stock indicators can usually be used to measure the scale, financial situation or sustainability of a certain field.

In the financial field, stock index is widely used in asset value, debt scale and market share. For example, in the stock market, the market value of a stock can be regarded as the stock index at a certain point in time. In the same fund industry, the total asset value is the total value of stocks, bonds and other assets held by the fund at a certain point, which is the stock index of the fund. Changes in the stock index can reflect the inflow or outflow of assets, and also have an impact on investors.

The stock index is also of great significance to enterprises and the government. Enterprises usually pay attention to the total sales, inventory and market share of their products or services to measure market performance and assets and liabilities. The government pays attention to stock indexes such as economic growth rate, unemployment rate and inflation rate, and understands the national economy and employment situation. Tracking and analyzing various stock indexes is helpful for enterprises and governments to make more effective management and decision.