example.com, example.net, and example.org are second-level domain names reserved by the Internet Engineering Task Force through RFC 2606, Section 3, for use in documentation and examples. They are not available for registration.
By implementing the reservation, the Internet Assigned Numbers Authority (IANA) made available domains to use in manuals and sample software configurations. Thus, documentation writers can be sure to select a domain name without creating naming conflicts if end-users try to use the sample configurations or examples verbatim.
When an address such as "email@example.com" is used to demonstrate the sign-up process on a website, it indicates to the user they should fill in an actual e-mail address at which they receive mail. "example.com" is used in a generic and vendor-neutral manner.