The main WHOIS database is run at the Network Information Center
(NIC). The whois command will let you search a database of every
registered domain (e.g. mit.edu) and of registered users. It's
primarily used by system postmasters or listowners to find the Points
of Contact for a site, to let them know of a problem or contact them
for one reason or another. You can also find out their postal
address. For example:
% whois mit.edu
Massachusetts Institute of Technology (MIT) MIT.EDU 18.72.2.1
Massachusetts Institute of Technology (MIT-DOM) MIT.EDU
Note that there are two entries for mit.edu; we'll go for the
second.
% whois mit-dom
Massachusetts Institute of Technology (MIT-DOM)
Cambridge, MA 02139