The PTR record
The PTR (pointer) record holds a pointer to a canonical name. This is most often used for reverse DNS lookups.
Here, we query for
PTR records of the domain
This unusual-looking domain name represents a reverse DNS lookup: instead of finding the IP for a domain name, we are asking for the hostname of an IP — in this case, the IP address
As expected, the DNS server responds with "localhost".
$ dog PTR 188.8.131.52.in-addr.arpa PTR 184.108.40.206.in-addr.arpa. 0s "localhost."