Index funds (ETFs) are “stocks” you can buy that track multiple individual companies. For example, the S&P 500 (stock ticker SPY) tracks the top 500 companies in the US. Buying SPY lets you invest in 500 companies at once, instead of having to buy each one individually. There are others, like tech-specific ETFs (QQQM), international, defense, etc. They provide a wider coverage and are less risky than, say, buying only Amazon stock.
Equities would be a better term instead of stocks but yes this is true. Another thing would be index funds ≠ ETFs. ETFs are investment funds that trade on stock exchanges, and many of them track indexes. I also think you should note that indexes are good because they rebalance themselves. Not trying to be split hairs just thought it would be good to add some more clarity.