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.
Tip: FireFox users can bookmark the following URL http://neranjara.org/tools/ipwhois/ip/%s, then add a keyword to your new bookmark. Now using your new bookmark type in [keyword] 127.0.0.1 into your address bar.
