Intranets and Extranets are now words in common use.

An Intranet in the classical sense is a network restricted wholely within an organisation, though in many cases now staff in the field require access and authentication mechanisms can be used to extend the intranet outwards. Typically intranet servers will be protected by firewalls if there is any physical connection between them and the outside world. In sensitive areas there might be no external connectivity al all.

Extranets are basically intranets extended outwards to major clients and suppliers. A company might have an intranet for orders, with an 'outer shell' accessible by major clients but not the world in general. There are a number of ways of achieving this while maintaining security.