Server aliases are additional names for your virtual host. Unlike domain aliases, they are not added to your DNS zone, and are registered only with apache. For instance, if your virtual host name is cpwebhosting.net and you also would like it to be available at www.cpwebhosting.net, you should add www server alias to the cpwebhosting.net domain.

Thanx tcheck
how can we add a server alias ?

To add a server alias, do the following:

1. Select Quick Access in Account menu.
2. Click the Web Options icon to go to your web options page.
3. Click the Edit icon next to the domain you need.
4. Scroll down to the Server alias field and click the Add icon.
5. Enter server alias. It will be added to the list of server aliases for this virtual host name.