INTERNET

The Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet. 

Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which local services to make available to the global Internet community. Remarkably, this anarchy by design works exceedingly well. There are a variety of ways to access the Internet. Most online services offer access to some Internet services. It is also possible to gain access through a commercial Internet Service Provider (ISP).

Source: http://www.webopedia.com/TERM/I/Internet.html

INTraNET

An intranet is a private network (private network) that uses Internet protocols (TCP / IP), to share confidential information within a company or operating company to its employees. Sometimes, the term intranet refers only to services that are visible, the company’s internal Web site. To build an intranet, a network must have some components that build the Internet, the Internet protocol (TCP / IP, IP address, and other protocols), the client and the server. HTTP protocol and several other Internet protocols (FTP, POP3, or SMTP) protocol is generally a component that is often used.

Generally, an intranet can be understood as a “personal version of the Internet”, or as a version of the Internet that are owned by an organization.

Source: http://www.adityaaji.com/networking/intranet-network/

extraNET

A buzzword that refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view.

Extranets are becoming a very popular means for business partners to exchange information.

Source: http://www.webopedia.com/TERM/E/extranet.html

internetwork

The art and science of connecting individual local-area networks (LANs) to create wide-area networks (WANs) , and connecting WANs to form even larger WANs. Internetworking can be extremely complex because it generally involves connecting networks that use different protocols. Internetworking is accomplished with routers, bridges, and gateways.

Source: http://www.webopedia.com/TERM/I/internetworking.html