DNS Stands for Domain Name System. DNS is one of the most important part of internet. All the computers on the internet are connected to each other and each one of them has a unique IP address and DNS maps these IP address with their Domain names. It is easier to remember and recall names than a bunch of numbers.
Whenever you try to browse a website on a browser like http://184.108.40.206, the browser uses DNS to get the IP address of the website asknetsec.com and then connects to that IP address and downloads the webpage.
DNS communication works in a server-client model where the client is the computer that needs to resolve a domain name to an ip address and the server is a computer which has the information about Domain name to IP address mappings.
A typical DNS transaction is made up of 2 packets. A request from the client to the server and a response from the server to the client. The request packet consists dns query for the domain name and the response packet consists of answer to that query in the form of IP address for the requested domain name.
Below is a typical DNS request and response packets taken from Wireshark that shows more info on the content of the DNS transaction.
The DNS query contains the domain name and DNS response contains the IP address associated with that domain name.