The domain name system is a distributed database arranged hierarchically. Its purpose is to provide a layer of abstraction between other Internet services (web, email, etc.) and the numeric addresses (IP addresses) used to uniquely identify any given machine on the Internet.

This has several advantages:

• It permits use of names instead of numbers to identify hosts (usually servers). Names are much easier to remember.
• It permits a server to change numeric addresses without requiring notification of everyone on the Internet, by simply retargeting a name to the new numeric address.
• One name can refer to multiple hosts, to share the load.

There are more benefits, of more esoteric nature.

This is all accomplished using resource records, which are organized into zones, which are in turn hosted by authoritative name servers.