A network linking computers within a given organisation, which is closed to outsiders. Its structure and user interface are based on those of the Internet.
A local area network, which may not be connected to the Internet, but which has some similar functions. Some organizations set up Web servers on their own internal networks so employees have access to the organization's Web documents.
Intranets use the same protocols and tools of the Internet but are privately developed and operated within an organisation.
A network based on TCP/IP protocols belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An Intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an Intranet fends off unauthorized access.