DNS is an acronym for Domain Name Server
As the Wiki explains, Domain Name system (DNS) is like the phonebook for the internet - it pairs easily referenced domain names with their more technical IP (internet protocol) address so you don't have to remember random numbers like 220.127.116.11 (google.com). Imagine what your world would be like if you had to enter that sequence of numbers every time you wanted to search for cute cat videos. Not cool.
Like having the wrong number in a phonebook will have you miss important phone calls and frustrate potential customers, improper or inefficient DNS can create a host of problems for your brand. You work so hard to get people to take interest in your company, why put hurdles and roadblock in front of them when they try and find you on the web.