Framework in general sense is a foundation on which you can build more complex applications.
Examples: a. Struts, Spring MVC, Tapestry for the purpose of web application development(closer to the client) b. Hibernate, JDO for data access. c. Google Web Toolkit(GWT)for rapid development of AJAX based clients.
They definitely improve the time to market aspects of a development cycle & are proven and reliable due to many development iteration cycles and larget test audience.
You may want to look into Jt as well (a J2EEpattern oriented framework). It implements many well-known design patterns including DAOs and adapters for several J2EE technologies (EJBs, Web Services, etc.). The URL is http://jt.dev.java.net/