Let’s take Apple (AAPL) for example, which is listed on the NASDAQ stock exchange. Apple currently has 4.6 billion shares outstanding, of which 4.35 billion are available to be traded (also known as the “float”). Using today’s closing price of $201.75 (July 11th, 2019), Apple has a market cap of $937.44 billion. That’s a big company! (By the way, market cap is a simple way to gauge the value of a company. If you bought every available share of stock, the market cap is how much it would cost you to buy the entire company.)
The movements of the prices in a market or section of a market are captured in price indices called stock market indices, of which there are many, e.g., the S&P, the FTSE and the Euronext indices. Such indices are usually market capitalization weighted, with the weights reflecting the contribution of the stock to the index. The constituents of the index are reviewed frequently to include/exclude stocks in order to reflect the changing business environment.
As of 2015, there are a total of 60 stock exchanges in the world with a total market capitalization of $69 trillion. Of these, there are 16 exchanges with a market capitalization of $1 trillion or more, and they account for 87% of global market capitalization. Apart from the Australian Securities Exchange, these 16 exchanges are based in one of three continents: North America, Europe and Asia.
A local financial regulator or competent monetary authority or institute is assigned the task of regulating the stock market of a country. The Securities and Exchange Commission (SEC) is the regulatory body charged with overseeing the U.S. stock markets. The SEC is a federal agency that works independently of the government and political pressure. The mission of the SEC is stated as: "to protect investors, maintain fair, orderly, and efficient markets, and facilitate capital formation."