A framework application is a business application — defined through an application rule and one or more rulesets — that provides an almost complete solution for a business.
As a best practice, framework applications are started through the Application Express. An "implementation" application, built upon the framework, extends and modifies a framework application for a specific organization, division, or organizational unit.
Do not confuse framework applications with solution frameworks — starter applications for specific industries and business functions — provided by Pegasystems.