The Internet is conceptualized as allowing any user to connect to any other user, even if they've never had any communication before and never will again after the connection
…is terminated. An extranet, in contrast, is usually used by several organizations to share data with each other in a trusted relationship; this usually involves IP tunneling to keep their information relatively secure while in transit over the public Internet. An extranet can also be used by outside users to participate in an intranet as if they were actually at the location of the intranet (which is a private network used within an organization); this is conceptually similar to VPN connections. (MORE)