World Wide Web or WWW refers to all the public websites or pages that users can access on their local computers and other devices through the internet 

An intranet is a private network that organizations use to share information between employees securely. They are web-connected sites on networks, such as Local Area Networks (LANs) or wide area networks (WANs). They can be better understood and visualized as a smaller version of the internet 

An extranet is an Intranet that is able to be accessed on the Internet in a secure way. This can be accessed anywhere in the world and access can be given to a company's suppliers or customers with different levels of access.