What is the definition of Market capitalization?

Market capitalization is the market value of the issued equity of a firm. It is calculated by multiplying the number of shares in the market by the price per share. Market capitalization is typically used to assess the size of the firm in question, the rough categories are:

• Small Cap - $2 billion or less
• Mid Cap - $2-10 billion
• Large Cap - $10 billion or more

As of 19th October 2011, the companies with the two largest market caps in the world are Apple Inc. (AAPL) and Exxon Mobil (XOM).