A website is uniquely idenfied by a domain name.
A domain has two parts (f.e. www.whatishttp.com):
a) whatishttp - This is the first part of the domain and can be your name or your company name
b) com - This is called the extension. Other extensions are: .net, .org, .biz, .info, mobi., .gov, .edu
.com - Commerce .net - Network
.org - Organization
.biz - Business
.info - Information
.mobi - sites easy viewed on mobile devices
.gov - Government
.edu - Education
.at - country code for Austria.
.be - country code for Belgium
.co.nz - country code for New Zealand.
.co.uk - country code for the United Kingdom
.uk.com - alternate domain for the United Kingdom
.de - country code for Germany
.de.com - alternate domain for Germany
.eu - country code for the European Union
.eu.com - alternate domain for the European Union
.us - American Web sites
.us.com - alternate domain for the United States
WHOIS is a protocol based on the TCP (transfer control) protocol. WHOIS can be used to obtain contact information about the owner of a domain. WHOIS is specified in RFC 3912.
Check out this application which uses the WHOIS protocol: Fast Whois