Subdomain In a domain name, the subdomain is that section which precedes the main domain name and is separated from it by a dot. For instance, in the domain blog.example.com, “blog” is the subdomain and example.com is the main domain. Subdomains organise different sections or functionalities of a website; blog-related sections, online stores, forums or other specific areas of activity on a website can be hosted by them. They are, however, treated by search engines like an independent entity, though they apply to the main domain. Proper choice of subdomain name is a matter of importance to branding as well as SEO.