The Domain Name System (DNS) is a hierarchical naming system constructed on a distributed database for any electronics connected to the Internet or other network.
The DNS translates domain names i.e. google.com (which are easy to remember for people) into numerical identifiers linked to specific IP addresses. This allows users to access devices located around the world using an easy to use domain name.
The DNS also stores other pieces of data including mail servers which accept e-mail on that particular domain.