The Domain Name System (DNS) is a standard technology for managing the names of Web sites and other Internet domains. DNS technology allows you to type names into your Web browser like compnetworking.about.com and your computer to automatically find that address on the Internet. A key element of the DNS is a worldwide collection of DNS servers. then, what is DNS server ?

A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts