Stock
A small piece of ownership in a company. Its price rises and falls with how investors value the business.
When you own stock, you own a share of a company's profits and assets. You can make money if the price goes up or if the company pays dividends.
Single stocks can fall sharply or go to zero. Many people own stocks through index funds instead, which spread money across many companies. Over long periods stocks have grown more than bonds or cash, but returns vary and some years are negative.