Source : WordNet®

intranet
     n : a restricted computer network; a private network created
         using World Wide Web software

Source : Free On-Line Dictionary of Computing

intranet
     
         Any {network} which provides similar services
        within an organisation to those provided by the {Internet}
        outside it but which is not necessarily connected to the
        Internet.  The commonest example is the use by a company of
        one or more {World-Wide Web} servers on an internal {TCP/IP}
        network for distribution of information within the company.
     
        Since about 1995, intranets have become a major growth area in
        corporate computing due to the availability of cheap or free
        commercial {browser} and {web server} software which allows
        them to provide a simple, uniform {hypertext} interface to
        many kinds of information and {application programs}.
     
        Some companies give limited access to their intranets to other
        companies or the general public.  This is known as an
        "{extranet}".
     
        (1997-07-14)