Add On Domain or Domain Pointer:

An additional domain name added onto your existing account.  This domain name is generally used to host a separate website within your main account.  You can configure the directory that will serve as this domain name's document root.  For instance, you can configure the following:

http://domainpointer.com points to http://maindomain.com/domainpointer

Note that when someone goes to domainpointer.com, they will NOT be redirected to maindomain.com/domainpointer.  Rather, they will continue to see domainpointer.com in their browser.  They will not be aware that they are visiting a site that is hosted underneath another domain.

Additionally, domain pointers have full email functionality (POP email accounts, email forwarders, mailing lists, etc).  You may also create subdomains of your pointed domain names.

Parked Domain:

A parked domain name is an additional domain name that can be "parked" on top of your main domain name.  In other words, when someone types in "parkeddomain.com" (assuming that is a parked domain name), they will see your main website.  You can NOT specify a new document root for parked domain names, and attempting to circumvent this with redirection is prohibited.

Parked domain names do not include any email or subdomain functionality.