What is Nslookup?

NSLOOKUP is a powerful network administrators command line tool available on many (if not most) operating systems for querying Domain Name Systems DNS, the tool is used to obtain the domain names or IP addresses, mapped against a name resource – so Name to IP, and IP to Name.

If you would like the full low down on NSLOOKUP please take a look on wikipedia

nslookup empsn.org.uk

nslookup 93.93.222.1

nslookup -type=ns empsn.org.uk

nslookup -type=ns empsn.org.uk
nslookup -type=soa
nslookup -query=mx
nslookup -type=any
nslookup -debug

Notes:
Authoritative answer – This is the answer that originates from the DNS Server which has the information about the zone file.
Non-authoritative answer – When a nameserver is not in the list for the domain you did a lookup on.
Different port – By default, the DNS servers use port 53.