ELI5: Explain Like I'm 5

Index fund

An index fund is like a basket filled with different investments. It is designed to contain a variety of investments, like stocks or bonds, that all match a specific part of the stock market. The goal of investing in an index fund is for the investments in the fund to grow over time, because generally the stock market grows over time. It's like putting your money in a big basket, instead of just one thing.