DotNetNuke is capable of serving many sites from a single installation. The term portal is often used to describe each site, although the term is somewhat narrow in its definition. So you might ask, what is a portal? The American Heritage Dictionary defines a web application portal as "a web site considered as an entry point to other web sites, often by being or providing access to a search engine." This can be true of DotNetNuke portals, but they really are more than just doorways to other applications or search engines — they also perform a host of other functions associated with displaying information to your users.
In DotNetNuke, a portal is one site, of n possible sites, in a single instance of DNN, with data and functionality completely discreet from other portals in the same instance. For the purposes of this discussion, a portal can be defined as the related data for one web site hosted within your DotNetNuke installation. The application natively provides the capability to host multiple web sites from the same code base, each containing different information and presented to the user at runtime based on the URL the user enters to access the code base. Exactly how the application accomplishes this task is covered later in the book.
As the portal administrator, you may set up hundreds of various web sites on the same portal. These can be a combination of parent and child portals (discussed later in this chapter), and at runtime the application will determine the proper content to display to the user based on the PortalID of the portal accessed. This is one of the most powerful features of DotNetNuke and has contributed to the rapid growth of the application since its inception.