authoritative server
also: nameserver, NS, zone server
A DNS server that holds the actual zone file and is responsible for answering authoritative answers about a domain's DNS records.
An authoritative server is a DNS nameserver that contains the original, master zone file for a domain. When a client queries an authoritative server, it receives a definitive answer marked with the AA (Authoritative Answer) flag, not a cached or delegated response.
For example, if you own example.com, your authoritative nameserver holds the actual records for that domain—such as the A records pointing to your web server IP, MX records for mail, and CNAME aliases. When someone looks up www.example.com, their DNS resolver eventually reaches your authoritative server, which responds with the real answer.
Authoritative servers are distinct from recursive resolvers (like your ISP's DNS or 8.8.8.8), which cache answers and forward queries. Most domains have at least two authoritative servers for redundancy, registered with a registrar and delegated via NS records at the root and TLD levels.