What is the meaning of ".com"?
There are about 185,000,000 people that search this question every year!
The simple answer: It is a top level domain for commerce.
It doesn't have any location assigned to it as some domains have and it doesn't even mean that you can buy anything on the site. It is recognised as the best and most popular extension. Due to it's popularity and lack of available domains the extension .co was released.
Anyone can use a .com domain, if you can find one that is available!