DoYouKnow: is reserved for a special purpose!

The domain which you come across daily in several tutorials and manuals, is a real one and is reserved by the Internet Assigned Numbers Authority (IANA). It is an organisation responsible for allocation of unique global domain names.

Have you ever checked it entering in the browser?

Not only this one, the  domains and are special domains which can be used without any permission in the documents for illustrative examples. These are neutral domains and are not available for registration.  The www subdomains like can also be used, but other subdomains like does not exist.

But why do we need special purpose domains for this, why not use some arbitrary names? Because, any domain you can think of may exist with some chance and  this may lead to naming conflicts. Moreover when you see [email protected], you immediately understand that it is a place holder and should be filled with a specific one.