DNS – (Domain Name System) the quick explanation;
Like a phone book for the internet – sort of –

Systems such as servers that are connected to a network, like the world wide web (www) or internet or even your own private network are assigned IP addresses much like your telephone number. While it may be easy for you to remember a few of your close family of friends phone numbers the more you add the more difficult it can be to remember so you buy a shiny new address book to store all those names and numbers organized in a meaningful manner.

Well DNS is sort-of like an address book for the web. It stores the name and numbers for interconnected resources, such as web site addresses and translates human readable names into machine readable addresses. When you launch your web browser and type in a web site address like www.google.com behind the scene your computer virtually opens its DNS address book to see if it know where to go find the site if your system doesn’t know then it reaches out to the next DNS server and so on until it finds the correct location and directs your browser to the right spot. There is technically a lot more going on behind the scene.

But hey.. why re-write the internet… the guys over at DYN did a great job explaining