Before discussing about the terms internet, intranet and extranet, we need to discuss the term Internetwork.
An internetwork can be defined as two or more computer networks (typically Local Area Networks LAN) which are connected together, usinng Network Routers.
Each network in an Internetwork has its own Network Address, which is different from other networks inside the Internetwork. Network Address is used to identify the networks inside an Internetwork.
Internetwork allows different users at different geographical locations of an organization to share data, resources and to communicate. Modern businesses cannot even function without Internetwork. Internet, Intranet and Extranet are different types of internetwork.
Internet, Intranet and Extranet
Internet: Internet is a worldwide, publicly accessible computer network of interconnected computer networks (internetwork) that transmit data using the standard Internet Protocol (IP). Internet is the world's largest Internetwork .
The terms World Wide Web (WWW) and Internet are not the same. The Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc. World Wide Web (WWW) is a collection of interconnected documents and other resources, linked by hyperlinks and URLs. The World Wide Web is one of the services accessible via the Internet, along with various others including email, file sharing, remote administration, video streaming, online gaming etc.
Intranet: An intranet is a private network that is contained within an enterprise. It may consist of many interlinked local area networks and use any Wide Area Network (WAN) technologies for network connectivity. The main purpose of an intranet is to share company information and computing resources among employees. Intranet is a private Internetwork, which is usually created and maintained by a private organization. The content available inside Intranet are intended only for the members of that organization (usually employees of a company).
Extranet: An extranet can be viewed as part of a company's intranet that is extended to users outside the company like suppliers, vendors, partners, customers, or other business associates.
Extranet is required for normall day-to-day business activities. For example, Placing order to registered vendors, Billing & Invoices, Payments, Joint Ventures, Product Brochures for Partners, Discounted price lists for partners etc.