IBM portlets are Web applications that runs in the context of the WebSphere Portal Server. They inherit from the javax.servlet.http.HttpServlet class and as such are treated as servlets by the application server. The portlet is executed inside a Web container managed by the application server. In the IBM Portlet API, this container is referred to as the Portlet container.
Note: It is not possible to directly execute the portlet functionality by addressing the portlet via http.
A portlet is visible on a portal page as a single small window, of which each portal page may have many. The portlet is the content inside the window, not the window itself. The window is defined by the selected skin.