Internet, Intranet and Extranet

In this article ,I want to explain the basic difference of internet, Extranet and intranet.because some one can not understand the simple concept of Internet, intranet and extranet.
Internet:
              Simple definition of internet is type of network which is a  combination of interlinked computers and any one can connect it through ISP.There is no restriction in internet.Public can connect to internet anywhere from the world .Internet is a public network.
 
Intranet: 
                      Network of an organization which can not be accessed by anywhere outside the network. Intranet is a type of private network which is locally accessed in the organization.Intranet connects to internet but fire walled so no one can connect to intranet from outside the organization.
 

Extranet:
               The main difference between intranet and extranet is that extranet can also be accessed outside the organization.Accessing other organization network is called extranet.For example In extranet  users,employees of organization and clients, accessing the network from other network.It involves LAN and WAN. IF a telecom company of Pakistan  access the NADRA network for verification of customer identification, it will achieve through extranet.