stock index
noun /ˈstɒk ɪndeks/
  /ˈstɑːk ɪndeks/
(North American English) (also share index British and North American English)
 [usually singular]- a list that shows the current value of shares on the stock market, based on the prices of shares of particular companies
- The S&P 500 stock index includes 500 large companies.