Official definition · 官方定义
“A stock index, also called a share index or stock market index, consists of constituent stocks used to provide an indication of an economy, market, or sector.”[1]
— Corporate Finance Institute, CFI Resource Library · corporatefinanceinstitute.com ↗ · accessed 2026-10-25
A stock index tracks the value of a group of shares using a fixed formula. Some weight companies by market value, some give each the same weight, and some use price alone. The index is a number, not a portfolio you can buy directly.
股票指数用固定公式追踪一组股票的价值。有的按市值加权，有的等权，有的只按价格加权。指数只是一个数字，不是可以直接买到的组合。
An index is a rule set, and the rule set determines returns. The S&P 500 is market-cap weighted, so its fate is increasingly tied to a handful of large companies; an equal-weight version of the same 500 stocks behaves differently. When you read that “the market fell 2%”, ask which index, which weights, and whether dividends are included.
指数是一套规则，而规则决定回报。标普 500 按市值加权，所以它的命运越来越依赖少数几家大公司；同样 500 只股票的等权版本，走势完全不同。
读到「大盘跌了 2%」时，要问：哪个指数、什么权重、含不含股息。
| Move变动 | Where it appeared出现位置 | What it means这句话在说什么 |
|---|---|---|
| — | US consumer sentiment sinks to its second-lowest level on record 股票指数 · 第 2 张术语卡 | The main index combines answers on personal finances, business conditions and buying plans. 读指数先问三件事：谁编的、问的是什么、基准年是哪一年。密歇根这个指数把 1966 年设为 100，所以 48.0 不是「48 分」，而是「不到 1966 年的一半」。 |
| 1.1% | Wall Street slumps as hot inflation revives the Fed’s rate-hike fears 股票指数 · 第 9 张术语卡 | ‘The S&P 500 dropped 1.1%’ is the headline number that sums up the day’s selloff for most Americans. 除标普 500 外，常用的还有道琼斯工业平均指数（30 家蓝筹）与纳斯达克综合指数（科技股为主）。指数跌 1.1% 即当日普跌。 |
The index is the economy
It is a set of listed companies, skewed to the largest and most globally exposed.
All indices are comparable
Weighting and selection rules change everything.
Index funds own the index
They own the constituents and replicate the rules imperfectly.
· the index rose 1.2%
· market-cap weighted
· equal weight
· index inclusion
· rebalance
the index rose 1.2% 指数涨 1.2%；market-cap weighted 市值加权；equal weight 等权；index inclusion 纳入指数；rebalance 再平衡。
· index vs ETF
· price return vs total return
index 是指数本身，ETF 是可交易的基金；price return 不含股息，total return 含股息。
The index gained X%, with the largest Y companies accounting for most of the move.
行情句：指数上涨 X%，最大的 Y 家公司贡献了大部分涨幅——account for 后面跟的是贡献度。
“The main index combines answers on personal finances, business conditions and buying plans.”
“‘The S&P 500 dropped 1.1%’ is the headline number that sums up the day’s selloff for most Americans.”