Whois is a tool that shows, on-screen, diverse information on a set domain: owner data, contacts, status, etc. In other words, everything a Whois database implies.
The way of using it is just as simple. You just have to insert a valid web address, or a hostname. The program also accepts IP addresses. The data appears in basic, already formatted format. You can also choose if you want the Whois header information to appear or not.