DNS

http://www.howtogeek.com/122845/htg-explains-what-is-dns/

DNS stands for “domain name system.” Domain names are the human-readable website addresses we use every day. For example, Google’s domain name is google.com. If you want to visit Google, you just need to enter google.com into your web browser’s address bar.

However, your computer doesn’t understand where “google.com” is. Behind the scenes, the Internet and other networks use numerical IP addresses (“Internet protocol” addresses). Google.com is located at the IP address 173.194.39.78 on the Internet. If you typed this number into your web browser’s address bar, you’d also end up at Google’s website.

We use google.com instead of 173.194.39.78 because addresses like google.com are more meaningful and easier for us to remember. DNS is often explained as being like a phone book – like a phone book, DNS matches human-readable names to numbers that machines can more easily understand.