From Paterva Wiki
This transform determines if an NS record exists for the given Domain. The NS record is the name server record and is returned as a NSrecord.This is normally used in the infrastructure footprinting of an organisation. A note of caution - it is not uncommon for organisations to unsource their name servers to their ISP or to the registrar of their domain. Thus - in terms of finding the network (e.g. resolving this to an IP address) of the target this has limited value - human inspection is advised.
Can be used in conjuction with the NSrecordToDomain_SharedNS transform as the first step to get the NS records for the domain.