How Do I Check is a Domain Name is Available?
The easiest way to determine if a domain name is available is to do a search on a registrar's website.
Registrars provide what is called a "whois" service.
Whois can tell you if a domain name is already registered and in some cases give you information about who registered in, business addresses and contact information. Some of this information can also be 'hidden' by purchasing privacy protection on domains which obfuscates the actual owner.
Note: For more technical users, you can also execute a whois query using the shell or command line utility on most computers.