A name server is a web server assigned with the sole task of sending and receiving request pertaining to domain names and IP addresses. The job of the domain name server is to take a number like an IP address and turn it into a readable term that can be typed into a browser's address bar, or vice versa.
Computers read Internet addresses much differently than humans. All computer language is in numbers and not letters. Therefore, in order for information to be transmitted from the nameserver to a user's computer, the DNS has to transmit information pertaining to the address and meaning of the domain name. The domain name system is a basically the largest database in the world, receiving more requests than any other database.