Reverse DNS, which is also commonly known as rDNS, is used to show which is the domain name corresponding to an IP address (IPv4 or IPv6). It is actually exactly the opposite process of the usual Forward DNS, where the purpose is to find the matching IP address for a domain name.
For achieving its goals and completing the process, rDNS requires using PTR records. rDNS is typically implemented to identify and validate that the IP address actually belongs to the specific domain name. That way, it is easier to avoid scams and spam emails. Read more about rDNS!