What is Stock Exchange?

Legal Definition
A stock exchange or bourse is an exchange where stock brokers and traders can buy and/or sell stocks (also called shares), bonds, and other securities. Stock exchanges may also provide facilities for issue and redemption of securities and other financial instruments, and capital events including the payment of income and dividends. Securities traded on a stock exchange include stock issued by listed companies, unit trusts, derivatives, pooled investment products and bonds. Stock exchanges often function as "continuous auction" markets, with buyers and sellers consummating transactions at a central location, such as the floor of the exchange.

To be able to trade a security on a certain stock exchange, it must be listed there. Usually, there is a central location at least for record keeping, but trade is increasingly less linked to such a physical place, as modern markets use electronic networks, which gives them advantages of increased speed and reduced cost of transactions. Trade on an exchange is restricted to brokers who are members of the exchange. In recent years, various other trading venues, such as electronic communication networks, alternative trading systems and "dark pools" have taken much of the trading activity away from traditional stock exchanges.

The initial public offering of stocks and bonds to investors is by definition done in the primary market and subsequent trading is done in the secondary market. A stock exchange is often the most important component of a stock market. Supply and demand in stock markets are driven by various factors that, as in all free markets, affect the price of stocks (see stock valuation).

There is usually no obligation for stock to be issued via the stock exchange itself, nor must stock be subsequently traded on the exchange. Such trading may be off exchange or over-the-counter. This is the usual way that derivatives and bonds are traded. Increasingly, stock exchanges are part of a global securities market.
-- Wikipedia
Legal Definition
The regulated and organized financial market where the buying and selling of securities occurs. Prices are set by supply and demand.
Legal Definition
A voluntary association of persons (not usually a corporation) who, for convenience in the transaction of business with each other, have associated themselves to provide a common .place for the transaction of their business; an (association of stock-brokers. Dos Passos, Stock-Brok. 14. The building or room used by an association of stock-brokers for meeting for the transaction of their common business.
-- Black's Law Dictionary