There are three main types of NAMESERVERS:

1) CACHING-ONLY name server does lookups of names, but controls no name records itself.
2) PRIMARY name server not only does lookups of names, but also owns the records for a domain.
3) SECONDARY name server does name lookups and it also backs up a primary name server by providing authoritative answers for a certain domain. Many name servers will combine Primary and Secondary functionality for different domains.