All name servers are caching servers. This means that the name server caches received information until the data expires. The expiration process is regulated by the time-to-live (TTL) field that may be attached to the data.
Additionally, you can set up a cache-only server that is not authoritative for any zone. A cache-only server is a server that is not a master server for any zone other than the in-addr.arpa. domain. A cache-only server handles the same kind of queries from clients that authoritative name servers perform. But the cache-only server does not maintain any authoritative data itself.
A cache-only server requires less memory than an authoritative server, but cannot function by itself if no primary or secondary servers are available.