【中文版】

股票指数是一种衡量股票市场整体表现的方式。它是由一系列股票价格根据一定的权重加权平均得到的，反映股票市场的整体涨跌情况。

股票指数的计算方法通常是根据每个股票的市值大小，来确定其在指数中的权重，然后将这些股票的价格进行加权平均得到指数值。其中，市值较大的股票在指数中的权重较大，对指数的影响也较大。

股票指数的作用是帮助投资者了解整个股票市场的整体表现，以及市场趋势和投资机会。通过观察股票指数的变化，投资者可以了解市场的大致走向和投资风险，从而更好地制定投资策略和决策。

在中国，最著名的股票指数是沪深300指数，它涵盖了沪深两市的市值最大、流动性最好的300只股票。此外，还有上证指数、深证成指等也较为知名。

总的来说，股票指数是衡量股票市场整体表现的重要指标，对于投资者来说具有重要的参考价值。

【英文版】

What is stock index? Stock index is a way to measure the overall performance of the stock market. It is obtained by weighted average of a series of stock prices according to certain weight, reflecting the overall rise and fall of the stock market.

The calculation method of stock index is usually to determine the weight of each stock according to its market value, and then weighted average the prices of these stocks to get the index value. Among them, stocks with larger market values have a greater weight in the index and have a greater impact on the index.

The function of stock index is to help investors understand the overall performance of the entire stock market, as well as market trends and investment opportunities. By observing the changes of stock index, investors can understand the general direction of the market and investment risks, so as to better formulate investment strategies and decisions.

In China, the most famous stock index is the CSI 300 Index, which covers the 300 largest and most liquid stocks in both Shanghai and Shenzhen stock exchanges. In addition, there are also well-known indexes such as the Shanghai Index and Shenzhen Component Index.

In general, stock index is an important indicator to measure the overall performance of the stock market, which has important reference value for investors.