A subdomain is
A subdomain is – the part of a domain that is appended to the beginning of the domain name, like a prefix. For example, if your domain URL is “specifydomains.com,” you can add a subdomain to the front of it to make “securepaynet.specifydomains.com” You can also add more than one level of prefix; “another.securepaynet.specifydomains.com”, for example. As with a regular domain, you can forward a subdomain to another URL. Subdomains can be up to 25 characters.
A subdomain is an easy way to create a memorable Web address for unique content areas of your site. For example, you could create a subdomain for pictures on your site called “pics” that is accessible through the URL pics.example.com in addition to www.example.com/pics.
You can have as many subdomains as you want, ALL for that low cost of a domain name at Shop.SpecifyDomain.com.
The HELP Center makes it easy! Keep in mind that where you host your domain is where you control subdomains.
More on domains.