are a formal Internet address within a domain, such as subdomain.yourdomain.com.
A subdomain is essentially a secondary virtual server for your primary domain. It follows the pattern similar to 'subdomain.domain.com' (assuming your domain is 'domain.com'). Each subdomain is mapped to directory in the root of your primary domain's website. Subdomains are available as a paid option.
The Subdomain feature allows you to create third level domain names from your main domain name. These subdomains can host completely different content from the main domain, since the content is stored in a different folder. Example: something.yourdomain.com