A portal is a user-facing aggregation point where multiple, potentially unrelated functionalities and services are housed. More generally, a portal can be thought of as a gateway to a variety of resources. Usually, the user is able to manage these resources by simply adding or removing them. This allows users to customize the portal to fit their needs and interests.
A variety of portal types exist, including consumer portals, corporate employee portals, and business partner portals. They all have the same purpose: to provide a single point-of-entry or gateway to a variety of resources that are important and relevant to their users.