Translates domain names to IP addresses. DNS stands for Domain Name System.
From Wikipedia:
The Domain Name System (DNS) is a hierarchical naming system built on a distributed database for computers, services, or any resource connected to the Internet or a private network. It translates domain names meaningful to humans into the numerical identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.
In addition, since there is no currently no way to authenticate that the reply is really from the DNS server that was queried, there is a proposal (DNSSEC) that will add support for cryptographic signing to all DNS requests (for validation purposes, the data itself would not be encrypted).
