Internetworks: Internetworks are the links to two or more networks. It means it connects two or more individual networks using various devices such as routers, bridges, and gateways. For example, the Internet.
Intranets and Extranets: Intranets is a telecommunication network that is designed to be open, but is secured with internal networks whose web browsing software provides easy point-and-click access by their users to multimedia information on the internal internet sites.
Whereas Extranets are also a telecommunication network that links intranet resources of a company with other organizations and individuals.
More info: What is Access Level?
