Common stock is a form of corporate equity ownership, a type of security. The terms voting share and ordinary share are also used frequently in other parts of the world; "common stock" being primarily used in the United States. They are known as Equity shares or Ordinary shares in the UK and other Commonwealth realms. This type of share gives the stockholder the right to share in the profits of the company, and to vote on matters of corporate policy and the composition of the members of the board of directors.
It is called "common" to distinguish it from preferred stock. If both types of stock exist, common/equity stockholders usually cannot be paid dividends until all preferred/preference stock dividends are paid in full; it is possible to have common stock that has dividends that are paid alongside the preferred stock.
In the event of bankruptcy, common stock investors receive any remaining funds after bondholders, creditors (including employees), and preferred stockholders are paid. As such, common stock investors often receive nothing after a liquidation bankruptcy Chapter 7.
Common stockholders can also earn money through capital appreciation. Common shares may perform better than preferred shares or bonds over time, in part to accommodate the increased risk.