Portlet bridge acts as an translation engine between portal environment and Java web framework to allow portlet development in desired Java framework and not in portal technology itself.
The portlet bridge acts as the translation engine between the portlet environment and the targeted system. It expresses the portlet request context to the bridged environment, executes the request and transforms the response as appropriate for the portlet environment.
It provides an abstraction of the portlet environment for the bridged environment, and for developers working within the bridged environment. These developers are free to execute Faces views as portlets, without the need to understand the details of the portlet APIs and development model.
There are many implementations of portlet bridge like a JSF PortletBridge (JSR-301 and JSR-329), GWT PortletBridge, Wicket PortletBridge and others.
Source: StackOverflow question, "What does a portlet bridge do?"
