The second level domain label example for the top-level domains com, net, and org was reserved in 1999 by the Internet Engineering Task Force in RFC 2606, Section 3, while it was reserved for the edu domain by the Internet Corporation for Assigned Names and Numbers (ICANN) since 2000.
By implementing the reservation, the Internet Assigned Numbers Authority (IANA) made available domains to use in technical and software documentation, 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 email address at which they receive mail. Example.com is used in a generic and vendor-neutral manner.