for questions that relate to stock markets. A stock market is a network of financial transactions, not a physical facility or discrete entity, for the trading of company stock.
A stock market or equity market is a public entity for the trading of company stock (shares) and equity derivatives at agreed upon prices. This includes securities listed on a stock exchange as well as those only traded privately.
The size of the world stock market was estimated at about $36.6 trillion in October 2008. The world derivatives market has been estimated at about $791 trillion nominal value, 11 times the size of the entire world economy. 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, as the latter refers to an actual value. Also, many derivatives are relatively illiquid, thus valued as marked to model, rather than an actual market price.
Stock market via Wikipedia