difference between main thread and child thread?

in jsp 7 implicit objects are available those are 1:response->This denotes the data included with the HTTP Response. 2:request->This denotes the data included with the HTTP Request. 3:out->This denotes the Output stream in the context of page. 4:Session -> This denotes the data associated with a specific session of user. 5:config->This is used to get information regarding the Servlet configuration, stored in the Config object 6:Application 7:page