Have you ever wondered what the domain example.com is all about? If you visit www.example.com, you’ll see an interesting web page that has information about its purpose. Click on the link ‘More information…‘ and you will be redirected to this URL: https://www.iana.org/help/example-domains.
Example.com is just one of a number of reserved domains for use in documentation. Other domains include example.net and example.org. The domains are reserved by the Internet Assigned Numbers Authority (IANA). These domains are documented in RFC6761.
It is therefore safe to use example.{com/.net/.org} for documentation purposes. We use it to write documentation on a variety of configurations for various software that are network- and internet-related.
In your spare time, read RFC6761. It’s fun!