Extranet and Intranet
An Extranet is a type of Intranet (Internal TCP/IP Network) that has been selectively opened to a firm's suppliers, customers.
Intranet
An intranet can be defined as a network connecting an affiliated set of clients using standard internet protocols, esp. TCP/IP and HTTP or as an IP-based network of nodes behind a firewall, or behind several firewall linked by secure, possibly virtual, networks.