Is WordPress a framework?
Not really. WordPress is a content management system.
WordPress can be used as a development framework, but it doesn’t really fit the generally-accepted definition of a framework, because it is too specific.
A framework is usually thought of as a generic app template, with few — if any — application-specific features. WordPress, on the other hand, is already a full-fledged CMS application.
However, it can be used as if it were a development framework, building new features as plugins. This can be a useful approach for applications that have a strong “content orientation” — such as (for example) project management or social networking applications.