A name server is a computer that holds your websites. When you register a domain, you would have to provide name servers to tell the registry where your website is located. If I was to have my own hosting company, the following name servers will be used.
- ns1.fsp.host
- ns2.fsp.host
- ns3.fsp.host
- ns4.fsp.host
The more name servers you have associated with your domain, the greater the chance of your site to stay up even if 1 or 2 servers are down for whatever the reason.