What is a WHOIS search?

When a domain name is registered, the Internet Corporation for Assigned Names and Numbers (ICANN) requires the domain name registrar of that domain to submit the buyers personal contact information to the "WHOIS" database. Once the listing appears in WHOIS directory, it becomes available for public searches using a WHOIS search tool.

You can now use the who.is.com search tool to find the status of a given domain name.
Each lookup will first determine the availabilty of the given domain. You will then have the option to view all available detailes of the domains WHOIS info or purchase it if it's available.