Domain alias

An "alias" is another name for the same thing.  It is a pseudonym. 

A "domain alias" is a second (or third or fourth) domain name - closely related to your first.  Examples: cozahost.co.za is a domain alias of cozahost.com.  google.co.za is a domain alias of google.com.

For example, you might register the domain name mybusiness.com and then realize that you want the mybusiness.co.za domain name too. 

Since you are already hosting mybusiness.com as "main" domain, you can add mybusiness.co.za as a domain alias TO mybusiness.com.

A domain alias is an alias (or pseudonym) in every sense of the word.  All email addresses, web addresses, or even server addresses that exist for the main domain also AUTOMATICALLY exist for the domain alias. 

For example if you create the email account name@mybusiness.com then name@mybusiness.co.za also automatically exist.  The same is true for a web page, ie http://www.mybusiness.com/home.html is exactly the same thing as http://www.mybusiness.co.za/home.html.

When two domains are hosted on the same web server and they are NOT related (ie you run two separate businesses), the second domain is typically paced in a folder of it's own and a redirect script (cozahost will supply on request) on the main site will direct visitors to the correct content automatically. 

Depending on your hosting package, you can add several domain aliases - to protect alternate spellings of your domain name or even to run multiple web sites from the same server.