DNS server:

Domain Name Service is an Internet-wide distributed database system that documents and distributes network-specific information, such as the associated IP address for
a host name, and vice versa. The host that stores this database is a name server. The library routines that query the name server, interpret the response and return the information to the program that requested it are resolvers.
For example: To determine the location of a remote computer on the Internet, communications software applications (such as NCSA Telnet) use resolver library routines to query DNS for the remote computer's IP address.