What is Stock?
Stock is a piece of ownership in a publicly held company. If you have the money, you can become an owner of Google (NASDAQ: GOOG), Microsoft (NASDAQ: MSFT), McDonald's (NYSE: MCD), Disney (NYSE: DIS) or Walmart (NYSE: WMT). Of course if you buy a single share of Google, you're not the only owner - there are almost 260,000,000 total shares of Google.
Even as the owner of a single share, you have rights as an owner (also called a stockholder). The company is required to report their financial condition to you. Most will even give you a vote (though in the case of Google, it's only one vote out of 260,000,000!) on who sits on the company's Board of Directors who run the company.
Best of all, if a company gets into financial trouble, you are not responsible, even if a company loses millions of dollars. The price of your stock might go down (and could even drop to zero), but that's your only risk.