CNAME stands for Canonical Name. CNAME records can be used to alias one name to another. CNAME records are typically used to map a subdomain such as www or mail to the domain hosting that subdomain's content.
To use CNAME records, select CNAME from the Add Record drop down in the advanced editor. Then enter the hostname you would like to alias from and the fully-qualified domain name you would like to alias to. You may also enter @ in the Alias for field to represent the domain itself.
A CNAME record can map the web address www.example.com to the actual web site for the domain example.com. For example, if the domain were example.com and you wanted www.example.com to point to example.com you could put www in the name field and @ in the alias for field.
For example, if you have a server where you keep all of your documents online, it might normally be accessed through docs.example.com. You may also want to access it through documents.example.com. One way to make this possible is to add a CNAME record that points documents.example.com to docs.example.com. When someone visits documents.example.com they will see the exact same content as docs.example.com.