Stock Market (Economy) 

The expression 'stock market' refers to the mechanism that enables the trading of company stocks (collective shares), other securities, and derivatives. Bonds are still traditionally traded in an informal, over-the-counter market known as the bond market. Commodities are traded in commodities markets, and derivatives are traded in a variety of markets (but, like bonds, mostly 'over-the-counter').

The size of the worldwide 'bond market' is estimated at $45 trillion. The size of the 'stock market' is estimated at about $51 trillion. The world derivatives market has been estimated at about $480 trillion 'face' or nominal value, 30 times the size of the U.S. economy…and 12 times the size of the entire world economy. It must be noted though that the value of the derivatives market, because it is stated in terms of notional values, cannot be directly compared to a stock or a fixed income security, which traditionally refers to an actual value. (Many such relatively illiquid securities are valued as marked to model, rather than an actual market price.)

The stocks are listed and traded on stock exchanges which are entities (a corporation or mutual organization) specialized in the business of bringing buyers and sellers of stocks and securities together. The stock market in the United States includes the trading of all securities listed on the NYSE, the NASDAQ, the Amex, as well as on the many regional exchanges, the OTCBB, and Pink Sheets. European examples of stock exchanges include the Paris Bourse (now part of Euronext), the London Stock Exchange and the Deutsche Börse.

Source: Wikipedia