Reverse DNS Lookup tools resolves a given IP to Host. The resolved host is the public host behind that ip. This tool is also called IP to Hostname or Reverse DNS Tool.
Reverse DNS Check tool queries the given ip to resolve to a hostname. The host name is anything like a normal domain or sub-domain i.e google-public-dns-a.google.com. This hostname resulted in querying the ip 8.8.8.8 which is Google's public dns ip. Whereas if you enter your own ip, it might point to the hostname of your ISP, or if you query your server's ip it might show you your domain name on which it resolves. This tool is named "Reverse DNS" just because it is run as a reverse process of resolving hostname to ip just like a normal dns check.
