Authoritative Name Server (ANS) is a commercial authoritavtive-only DNS server software product from Nominum, a company founded to create commercial DNS and DHCP software. It is advertised as 100% uptime, high-performance DNS software, suitable for the largest of DNS operators.
When not referring to the Nominum software product, the term authoritative name server is used to describe a DNS server which provides authoritative answers to queries. See Name Server for full details.