Resolve Permissions Errors Step #7
An "Intranet" is private. It does not allow devices connected -to it- to connect through it and interact or communicate with other devices that are accessing the World Wide Web.
An "Extranet", is much the same, except it's not, because it does not restrict devices from connecting to the World Wide Web through it/s servers, or it is connected to a device that is connected to the internet. This means that the servers on an "Extranet" are accessible -through one method or another- by device(s) "outside of the netwrok". Which makes them vulnerable to hacking or attacks or intrusions of some sort, by any device on the internet.
The "Internet" is public domain... outside of your ISP turning on, or off, your internet connection, there is no security or denial of service/connection. Assuming your device can connect by Wifi, or gain access through a CAT5 Cable, you are on the internet.
So an extranet is an intranet which has a router in place to protect the devices connected to it, from being accessed by the internet, yet allows the intranet to access the internet. This could technically snare a philosophical person in the debate of whether all extranets are internets or all internets are extranets... And this is why it was mentioned on the previous page that there are technically two types of networks.
That is the "simple" define of the difference in network types.
For those that learn better from picture books our next step will assist you a bit better in understanding.