It is a name. However in common usage we are often referring to the most basic part of a group of domain names
(e.g. info.na being the domain behind the names www.info.na and ftp.info.na and http://info.na/ ).
In this sense it is more like an address (no 7 some street) for an infinitely expandable house
(so you can just keep adding room numbers :-).

A domain name, is a series of textual characters that identifies a specific IP address,
uniquely identifies a website on the Internet.
Domain names locate businesses, organizations, or other entities on the Internet.
Domain names are easy to remember, easy to type alternatives
to obscure URL's that you receive with free website hosting services.

Using a domain name allows you to receive more visitors,
less bounced emails, and the chance to make a lasting impression on the Web.

A great benefit of using your domain name is that
regardless of how many times you change your access provider,
your Email and website address will always remain the same.