A framework is an existing library or set of libraries to help you complete a common task faster and more easily. Use this tag if you're writing a framework, not if you're just using one. When using a framework the specific framework should be used instead of this tag.
A framework is a set of code or libraries which provide functionality common to a whole class of applications. While one library will usually provide one specific piece of functionality, frameworks will offer a broader range which are all often used by one type of application. Rather than rewriting commonly used logic, a programmer can leverage a framework which provides often used functionality, limiting the time required to build an application and reducing the possibility of introducing new bugs.