What is the DNS
When using the Internet, users access resources using names. For example, if you were to go to Netnod’s website, you would go to www.netnod.se. However, the computers that make up the Internet know these resources instead by numeric addresses. They see www.netnod.se as either 126.96.36.199 or 2a01:3f0:1:3::109, depending on which version of the Internet protocol they’re using. That name to number translation is done by the Domain Name System, or DNS.
Read or download (PDF): Netnod Fact Sheet - What is the DNS?