Domain Parking:

You can set up a domain name that you own to point to another domain name. This is known as "parking" a domain.

Example: You own the test.com and test.net domain names. You already have a web site for test.com, but you do not want to create a new web site for test.net at the moment. By parking test.net on top of test.com, all URLs for test.net will automatically go to test.com instead.

The nameservers for the domain test.net should be the same as test.com.