A stock market is a market for the trading of company stock, and derivatives of same; both of these are securities listed on a stock exchange as well as those only traded privately.
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The term 'the stock market' is a concept for 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 $300 trillion. The major U.S. Banks alone are said to account for about $100 trillion. It must be noted though that the derivatives market, because it is stated in terms of notional outstanding amounts, cannot be directly compared to a stock or fixed income market, which refers to actual value.
The stocks are listed and traded on stock exchanges which are entities (a corporation or 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.