The intranet is a network within an organization that is accessible only to that organization's members, employees and authorized persons. This network uses Internet Protocol technology to share information, operational systems, or computing services within an organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network within an organization. Sometimes, the term refers only to the organization's internal website, but may be a more extensive part of the organization's information technology infrastructure, and may be composed of multiple local area networks. The objective is to organize each individual's desktop with minimal cost, time and effort to be more productive, cost efficient, timely, and competitive.

An intranet may host multiple private websites and constitute an important component and focal point of internal communication and collaboration. Any of the well known internet protocols may be found in an intranet, such as HTTP (web services), SMTP (e-mail), and FTP (file transfer protocol). internet technologies are often deployed to provide modern interfaces to legacy information systems hosting corporate data.

An intranet can be understood as a private analog of the Internet, or as a private extension of the internet confined to an organization. The first intranet websites and home pages began to appear in organizations in 1994-1996. Although not officially noted, the term intranet first became common-place among early adopters, such as universities and technology corporations, in 1992.

Intranets are sometimes contrasted to extranets. While intranets are generally restricted to employees of the organization, extranets may also be accessed by customers, suppliers, or other approved parties. Extranets extend a private network onto the internet with special provisions for authentication, authorization and accounting (AAA protocol).

In many organizations, intranets are protected from unauthorized external access by means of a network gateway and firewall. For smaller companies, intranets may be created simply by using private IP address ranges, such as 192.168.0.0/16. In these cases, the intranet can only be directly accessed from a computer in the local network; however, companies may provide access to off-site employees by using a virtual private network, or by other access methods, requiring user authentication and encryption.

Sourced: http://en.wikipedia.org/wiki/Intranet