There are several ways to define a web portal, the first definition would be as a web site that provides an access point to another web site, which provides access to a search engine. The definition is a good starting point, but it is difficult to change some of the ideas already formed in the world about what a web portal is.
The second definition would be as a web site (intranet or extranet) that combines information from multiple and scattered sources, providing a unique interface, in order to improve the use and provide powerful search capabilities.