This is a Whois service. There is a lot of websites that offers free Whois service. Whois shows info about domains or IP addresses ownership.
Reverse DNS translates IP addresses in usually FQDNs.
The link that Ross requested today (2/5/16) in class. Pretty Interesting!
If you purchase your own domain, make sure you use a provider that allows you to conceal your personal information. Whois can show all the information you gave to the provider when you purchased your domain. Most hosts will offer free Whois protection, hiding your information and substituting fields with the company's information. (I ran into this issue with all of my info being publicly available with a Whois).