(Domain Name System) A system for converting host names and domain names into IP addresses on the Internet or on local networks that use the TCP/IP protocol. For example, when a Web site address is given to the DNS either by typing a URL in a browser or behind the scenes from one application to another, DNS servers return the IP address of the server associated with that name.

In this hypothetical example, WWW.COMPANY.COM would be converted into the IP address 204.0.8.51. Without DNS, you would have to type the four numbers and dots into your browser to retrieve the Web site, which of course, you can do. Try finding the IP of a favorite Web site and type in the dotted number instead of the domain name!

A Hierarchy
The DNS system is a hierarchy of database servers that start with the root servers for all the top level domains (.com, .net, etc.). The root servers point to authoritative servers residing within ISPs and companies that resolve the host names to complete the name resolution. Using the example WWW.COMPANY.COM, COMPANY.COM is the domain name, and WWW is the host name. The domain name is the organization's identity on the Web, and the host name is the name of the actual Web server within that domain (see WWW). See DNS records, reverse DNS, DDNS, HOSTS file, mDNS, ping, root server and WINS.