Pointers, Add-Ons, and Subdomains?
Domain pointers, parked domains, domain alias or domain forwarders:
A domain pointer is an additional domain name that points to the root of your site, in other words, it allows you to point multiple domain names to the same website. Domain pointers are free but you need to pay for the domain registration and you must point them to the same name servers of your main domain.
Add-on domains:
An add-on domain is a secondary domain name that points to a folder (subdirectory) within the main hosting account. It will act as a full account; you can create sub-domains, email accounts, and FTP accounts for your addon domains and it can be added directly from your cPanel.
Subdomains:
Subdomains are a way of creating separate accounts within your main account.
The subdomain can be accessed through a separate URL in the form of http://subdomain.domainname. Subdomains are often used to make access to subdirectories easier by simply typing in a shorter domain name, rather than the full domain name and the directory name.