The Java Persistence API 2.1 Specification was developed under JSR-338. This section just gives you an overview of the improvements in the API. The complete document specification (for more information) can be downloaded from http://jcp.org/aboutJava/communityprocess/final/jsr338/index.html.
JPA (Java Persistence API) is a Java specification that aims to define the standard features of ORMs (Object-Relational Mappings). However, JPA is not a product but a set of interfaces that require implementations. The most well-known implementations are as follows: Hibernate, Toplink, OpenJPA, and EclipseLink, which is the reference implementation.
Briefly, we can say that an ORM is an API used to establish a correspondence between the object model and a relational database. It gives you the ability to handle the data of your database as if they were objects, without too much worry about the physical schema.