WHOIS

From Wikipedia:

WHOIS (pronounced "who is"; not an acronym) is a query/response protocol which is widely used for querying an official database in order to determine the owner of a domain name, an IP address, or an autonomous system number on the Internet. WHOIS lookups were traditionally made using a command line interface, but a number of simplified web-based tools now exist for looking up domain ownership details from different databases. Web-based WHOIS clients still rely on the WHOIS protocol to connect to a WHOIS server and do lookups, and command-line WHOIS clients are still quite widely used by system administrators. WHOIS normally runs on TCP port 43.

Lookup

Tip: FireFox users can bookmark the following URL http://neranjara.org/tools/whois/domain/%s, then add a keyword to your new bookmark. Now using your new bookmark type in [keyword] example.com into your address bar.