From Joomla! Documentation
|The Joomla! Framework was an important part of the Joomla! CMS architecture in the versions 1.5 and 1.6. It was based on modern object-oriented design patterns that make the Joomla core highly maintainable and easily extendable. Between April and July 2011, the Framework was rebranded as the Joomla! Platform and is now being developed separately from the Joomla! CMS. The first version of the CMS to ship with the Platform was version 1.7.
Third party developers benefit from the rich, and easily accessible functionality that the Joomla Framework provides.