DNS - Domain Name Server / Service

The Domain Name Service (DNS) stores and associates many types of information with domain names, but most importantly, it translates domain names (computer hostnames) to IP addresses. It also lists mail exchange servers accepting e-mail for each domain. In providing a worldwide keyword-based redirection service, DNS is an essential component of contemporary Internet use.
Note: the above is a quote from Wikipedia
DNS can also refer to Domain Name Server(s) refering to one or more servers that provide the Domain Name Service. are a part of the domain name system.
Domain Names are used to make using the internet easier for humans.

You type in a URL or click on a link
Your computer looks for a local HOST(S) file to translate that www.google.com address to an IP address

• (You understand and can remember www.google.com .. your computer only knows numbers ... that ones and zeroes thing ...)

Not found? Your computer looks for a local DNS cache file to do the look-up
Not found? Your computer sends a query to your ISP's DNS server to do the look-up
Not Found? That DNS request gets passed on to your ISP's upstream
Not found? That DNS request continues to get passed upstream, until 'someone' finally has the answer.

• (At present, the whole of the Internet is handled by 13 master DNS systems, located around the world)
• Typical data seen in a "DNS query" response;
  • dns 72.14.203.104
  • nslookup 72.14.203.104
  • Canonical name: ro-in-f104.google.com
  • Addresses:
  • 72.14.203.104

Finally found? Your computer then points your browser to (currently/possibly even for you) 72.14.203.104
HTTP data is transferred, your computer asks, Google's server replies, eventually you see a web-page on your screen

see also: rDNS

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