You can think of a domain as the top level of organization for the Web. Georgetown.edu and Google.com are domains. Addresses that start with these domain names are managed by the entity they represent. A domain is a part of a URL, usually coincides with the website’s name, like “Georgetown” in georgetown.domains.
A subdomain is a second website, with its own unique content, but there is no new domain name. Instead, you use an existing domain name and change the www to another name. Technically, Georgetown Domains users sign up for a sub-domain instead of a domain. The urls will be of the form [customizedname].georgetown.domain.
How to get a subdomain
Find the section of the Domains Dashboard that looks like the picture below. It offers several options for subdomains.