Nameservers (or Domain Name Servers) are the machines that perform the DNS function, containing zone files listing all the hosts on their network, and their corresponding IP addresses. If a nameserver is unable to determine which IP address a given hostname (i.e. www.rwgusa.com) should map to, it will at least be able to point to another nameserver, which will either contain the information, or pass the request on until the correct nameserver is found.
