What is a persistence framework?

Here are a few pointers and definitions for what is a persistence framework:
http://www.roseindia.net/enterprise/persistenceframework.shtml
A persistence framework moves the program data in its most natural form (in memory objects) to and from a permanent data store the database. The persistence framework manages the database and the mapping between the database and the objects. There are many persistence framework (both Open Source and Commercial) in the market. Persistence framework simplifies the development process.

http://www.pbell.com/index.cfm/2008/7/14/What-Should-a-Persistence-Framework-Do
At its simplest, the goal of a persistence framework is to simplify and speed up the process of handling persistence of your applications. What a persistence framework needs to do depends heavily on your use cases.

http://tinylearn.com/index.php?option=com_content&view=article&id=60&Itemid=73
It makes it easier to use a database with Java and .NET applications.
The persistence layer sits between the business logic layer of the application and the database. This separation is important to ensuring that your persistence strategy is not mixed with your business logic code, or vice versa. The benefit of this separation is that your code can be more easily maintained, as it will allow your object model to evolve independently of your database design.