A stock is a type of security that represents ownership in a company. When you buy a stock, you are buying a small piece of ownership in the company.
When a company issues stock, it is selling ownership in the company to the public. Companies may issue stock to raise money to finance their operations or to pay off debts. The price of a stock is determined by the supply and demand for it in the market. As a shareholder, you have the right to sell your stock at any time, although the price you receive will depend on the current market conditions.
There are two main types of stock: common stock and preferred stock.