One line definition of a Portal is - "Single interface to interact with enterprise applications, people, content, and processes"
WebSphere Portal provides (additional) services such as single sign-on, security, directory services, content management, personalization, search, collaboration, search and taxonomy, support for mobile devices, accessibility support, internationalization,e-learning, integration to applications, and site analytics.
We can customize the Portal to suit our needs.
Portal is an application which runs in the Application Server container
WebSphere Application Server enables Web transactions and interactions with a robust deployment environment for e-business applications. It provides a portable, Java-based Web application deployment platform focused on supporting and executing servlets, JavaBeans, JavaServer Pages (JSP) files, and enterprise beans.