What is the difference between Internet, Intranet, and Extranet?

Internet

Internet refers to the world-wide collection of independent networks, connected via routers to each other for communication purposes.

Intranet

Intranet refers to a collection of networks within a logical body, such as a building, corporation or other entity. Intranet

s can be as simple as two computers connected at home to each other, or as vast as 1000 branch offices of a bank, connected via privately owned, non-public network links. Intranets usually have a firewall and router, which permits access to the public Internet, while protecting the internal Intranet from malicious users.

Extranet

Extranets are collaborative meta-networks which are set up between two or more Intranets to facilitate business or research communication. An example would be General Motors and the many subcontractors

that supply GM with parts for their products. GM and it's partners establish links to tie each others Intranets together to better serve each others needs, such as secure communications for financial transactions, parts ordering, etc. Another example would be the Federal Reserve Bank, which maintains an Extranet connected to each of it's constituent banks for the transfer of funds.

Finally, the term 'internet' (lower case) is a generic description of a collection of networked devices.