DNS (Domain Name System) is a protocol within the TCP/IP protocol that uses a set of standards for how computers exchange data on the Internet and on many private networks.
The basic job of DNS is to convert a user-friendly domain name into an IP address that computers use to identify one another. Think of DNS like your cellphone contact list; you tap the name and the phone contacts to a phone number.
It is easier to remember flashrouters.com, rather than its IP address. Imagine if you had to remember all of the IP addresses of your favorite websites!