nslookup question

[nobody special]

I'm new here so please tolerate my nusance of a probably dumb question. When
we do a nslookup command of an ip address and it returns the dns name and
other bits of information, does it mean the dns client is alive on the net
or does it simply mean that the dns client is regestiered to a DNS server or
both? What I'm trying to understand  is, does the dns client have to be
alive in order for nslookup command to return data?

Rodney