A unique name that identifies a particular internet site such as www.xoops.org
On the Web, the domain name is that part of the Uniform Resource Locator(URL) that tells a domain name server using the domain name system (DNS) whether and where to forward a request for a Web page. The domain name is mapped to an IP address (which represents a physical point on the Internet).
When you buy a domain name, you will the option of connecting that name to a specific ip address that will be your website. Once the DNS has resolved (can take 48 hours or so) your website will load in the browser whenever you type your domain name.
Web hosts often supply the ip address and allow you to upload and install a website on the ip address before the domain has resolved. You can install a xoops website like this. HOWEVER, you must remember to change the site URL in mainfile.php from the ip address to the domain name once it has resolved, or else your site may not work properly.