An Intranet is private Internet. That is it uses all the same technology as the Internet, but to internal computers not "visible" from outside a "firewall". It is not really a "thing", just a way of describing the internal network of a company, hospital, or even a private home. For example, you could say "...those pictures are proprietary. And only published on our Intranet. To see them from the outside, you would need to have our virtual private network software installed.
