Objects with page scope are accessible only within the Page in which they're created. The data is only valid during processing/preparing of the current response.
Objects with request scope are accessible from all Pages processing the same request in which they were created.
A good example of Objects that might be given session scope would be user name and password. These would be accessible from all Pages processing a given request. They would no longer be available after a user logs out.
Objects with application scope are accessible from all JSP pages and Servlets that reside in the same webapp.
In the following example thevalue is set in app1.jsp and is available in all of the webapp j-siegel, in particular in app2.jsp and the Servlet persist.