Registrars require the use of name servers or hosts for every domain registered. Every domain name has to be linked to a name server for it to be valid. Some people do not have they own name servers, therefore a user must have domain name requests answered by someone. They must hold or 'park' domain name(s) for an amount of time.
Companies which register domain for you usually provide a nameserver for domains that do not yet have their own hosting.
Domain parketing provides a inactive space for a domain name. With the purchase of a hosting service, you can activate your domain name.