Subdomain

A subdomain is another part of a main domain that typically illustrates different parts of an organization. For example, blog.boostability.com would indicate that blog content would be available underneath the domain boostability with com being the top level domain or TLD.

Not all sites have subdomains and their use is a hotly debated topic in the SEO realm. Most SEO experts have the opinion that subfolders serve the same purpose and require less overhead to manage and, therefore, more preferable to subdomains.