A name server is a computer application that implements a network service for providing responses to queries against a directory service. It translates an often humanly meaningful, text-based identifier to a system-internal, often numeric identification or addressing component. This service is performed by the server in response to a service protocol request.

An example of a name server is the server component of the Domain Name System (DNS), the core namespaces of the Internet. The most important function of DNS servers is the translation (resolution) of human-memorable domain names and hostnames into the corresponding numeric Internet Protocol (IP) addresses, which can be routed in the Internet.

The Internet maintains two principal namespaces: the domain name hierarchy and the IP address system. The Domain Name System maintains the domain namespace and provides translation services between these two namespaces. Internet name servers implement the Domain Name System. The top hierarchy of the Domain Name System is served by the root name servers maintained by delegation by the Internet Corporation for Assigned Names and Numbers (ICANN). DNS servers, which are located all over the world, translate domain names into IP addresses, giving them control over which server a user may access via a given domain. Below the root, Internet resources are organized into a hierarchy of domains, administered by the respective registrars and domain name holders. A DNS name server is a server that stores the DNS records, such as address (A, AAAA) records, name server (NS) records, and mail exchanger (MX) records for a domain name (see also List of DNS record types) and responds with answers to queries against its database.

Name servers are usually either authoritative or recursive, as described below.

Although not the usual practice today, name servers can be both authoritative and recursive, if they are configured to give authoritative answers to queries in some zones, while acting as a caching name server for all other zones.

An authoritative name server is a name server that is responsible for giving answers in response to questions asked about names in a zone. An authoritative-only name server returns answers only to queries about domain names for which it is responsible (as specifically configured by its administrator).

An authoritative name server can either be a primary server or a secondary server. A primary server for a zone is the server that stores the definitive versions of all records in that zone. It is identified in the start-of-authority (SOA) resource record. A secondary server for a zone uses an automatic updating mechanism to maintain an identical copy of the primary server's database for a zone. Examples of such mechanisms include DNS zone transfers and file transfer protocols. DNS provides a mechanism whereby the primary for a zone can notify all the known secondaries for that zone when the contents of the zone have changed. The contents of a zone are either manually configured by an administrator, or managed using Dynamic DNS.

Every domain name appears in a zone served by one or more authoritative name servers. The fully qualified domain names of the authoritative name servers of a zone are listed in the NS records of that zone. If the server for a zone is not also authoritative for its parent zone, the server for the parent zone must be configured with a delegation for the zone.