In the Domain Name System (DNS) hierarchy, a subomain is a domain that is part of a larger domain. For example, "example.com" is a subdomain of the "com" top-level domain (TLD) while "www.example.com" is a subdomain in the domain "example.com". In fact, the "com" TLD is a subdomain of the root domain, ".". This hierarchical organisation is similar to that in a filesystem; something is a subdomain if it could be equated to a folder, and a record within that subdomain to a file. Note, though, that DNS names are written in descending hierarchy right-to-left, where filesystems are written left-to-right.