We use Portlet Define Objects <Portlet:DefineObjects> tag in our JSP code, while developing a portlet in Liferay. We generally use this tag to inherit the predefined objects in our JSP. By doing this, we get escape to write the entire code to include all these objects in oue JSP page.
JSR 168 (Portlet Specification 1.0)
In JSR 168, there are only three variables are defined:
1) RenderRequest renderRequest
2) RenderResponse renderResponse
3) PortletConfig portletConfig
The following taglib uri and defineObject tag should be used to include the above mentioned variables in the JSP page, according to JSR 168.