What is an Intranet

What is an Intranet?

An Intranet is a private computer network based on the standards of the Internet.

Intranets use Internet technologies to link together information resources of an organization; from text documents to multimedia documents, from legacy databases to document management systems. Intranets may also include network security, workgroup computing, bulletin boards and search engines.

An Intranet may extend across the Internet. This is usually done using a Virtual Private Network (VPN).

I understand what an Intranet is. What is an Extranet?