A portal is an online interface which allows users to access systems, databases, and/or enterprise applications.
A portal serves as an entry point for users, giving them permission to access specific information, such as emails, forums, or an online store. Unlike a website, a portal is a single web page which aggregates content and presents it in one place for visitors, sometimes requiring a login.
A web portal can provide a convenient, singular location for large amounts of information. For customers, a storefront-type web portal could allow them to browse products/services. Internally, web portals can provide employees with easy access to training manuals, company policies, emails, and more.
References
https://en.wikipedia.org/wiki/Web_portal