What is DNS?
DNS stands for Domain Name System. It is the process by which a domain entered into a web browser (www.netwisehosting.co.uk, for example) is able to find the server on which the required information is stored. It does this by contacting a DNS Server, which then points the enquirer towards the IP address associated with that domain. This is also known as normal or forward DNS.
Without DNS, everytime a user wanted to contact your servers, they would need to enter your machines IP address - not the most userfriendly of processes.
This idea can be taken a step further with Reverse DNS (rDNS) - you can read more about that by clicking here.