Definition of Root nameserver

A root name server is a DNS server that answers requests for the root namespace domain, and redirects requests for a particular  top-level domain (TLD) to that TLD's nameservers. Although any local implementation of DNS can implement its own private root name servers, the term "root name server" is generally used to describe the thirteen well-known root name servers that implement the root namespace domain for the Internet's official global implementation of the Domain Name System.