Index fund refers to fund products with specific indexes (such as Shanghai and Shenzhen 300 Index, Standard & Poor's 500 Index, Nasdaq 100 Index, Nikkei 225 Index, etc.) as the target. ) as the target index, and take the constituent stocks of the index as the investment object, build a portfolio by buying all or part of the constituent stocks of the index, and track the performance of the target index.

Generally speaking, a certain number of company stocks are selected according to a specific method (for example, according to the size of the company's assets) to form an index with these company stocks. A fund company selects a combination of some or all company stocks in the index as an index fund.

Index funds are divided into different types according to different forms. The simplest classification is broad-based index funds and narrow-based index funds.

Some common funds such as CSI 300, CSI 500 and SSE 50 are broad-based index funds, which represent the trend of the whole market.

In addition to broad-based index funds, there are also some narrow-based index funds, such as CSI Liquor, CSI Medicine 100, CSI Real Estate, CSI Environmental Protection, CSI Pension and other theme or industry index funds.