The document provides an overview of domain name servers (DNS) and their role in mapping domain names to IP addresses on the internet or private networks. It discusses DNS server hierarchy and the different types of DNS servers, including master, slave, caching-only and forwarding-only servers. It also defines terms like fully qualified domain name and the domains and sub-domains they contain. The document aims to introduce DNS concepts before explaining how to install and configure BIND, the most common DNS software on Linux systems.