A huge bunch of stuff on the skinny
Together, the name and extension must form a domain name no one else has registered. The Internet has a governing body, ICANN, which ensures each domain name is unique, and that the required information is collected during the Internet domain registration. The InterNIC website provides access to the database of Internet domain registration data. The registry itself is WHOIS. Fortunately, most Internet domain registrars provide a search to determine availability of the name you want.