DNS organizes names in a hierarchy, read right to left.
Take mail.google.com:
- "." (root): Top of the tree, mostly invisible
- "com": Top-Level Domain (TLD)
- "google": Second-level domain
- "mail": Subdomain
No single server knows all DNS records. Root servers point to TLD servers. TLD servers point to authoritative servers for each domain. This distribution makes DNS scalable and resilient.