What it is:
Mega cap is a designation for any company with a market capitalization in excess of $200 billion.
How it works (Example):
The largest companies in the world are referred to as mega caps because of their relative market size and value.
Any company worth more than $200 billion generally qualifies as a mega-cap company. Microsoft, Exxon and Wal-Mart are examples of mega-cap companies. Since market capitalization fluctuates with the company's stock price, companies can fall in and out of the mega cap classification.